Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $143.44   13.835%   $163.2849   $163.28   $163.30   $163.30  
  Purchase #2 $244.46   9.104%   $266.7156   $266.72   $266.70   $266.70  
  Purchase #3 $194.80   13.792%   $221.6668   $221.67   $221.65   $221.70  
  Purchase #4 $231.29   13.665%   $262.8958   $262.90   $262.90   $262.90  
  Purchase #5 $160.82   12.666%   $181.1895   $181.19   $181.20   $181.20  
  Purchase #6 $125.94   13.847%   $143.3789   $143.38   $143.40   $143.40  
  Purchase #7 $180.31   7.114%   $193.1373   $193.14   $193.15   $193.10  
  7 purchase totals = $1,281.06       $1,432.2688   $1,432.28   $1,432.30   $1,432.30