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 $112.93   12.773%   $127.3545   $127.35   $127.35   $127.40  
  Purchase #2 $31.38   7.257%   $33.6572   $33.66   $33.65   $33.70  
  Purchase #3 $13.50   11.165%   $15.0073   $15.01   $15.00   $15.00  
  Purchase #4 $215.99   3.693%   $223.9665   $223.97   $223.95   $224.00  
  Purchase #5 $87.26   9.847%   $95.8525   $95.85   $95.85   $95.90  
  Purchase #6 $242.66   6.122%   $257.5156   $257.52   $257.50   $257.50  
  Purchase #7 $137.52   6.370%   $146.28   $146.28   $146.30   $146.30  
  7 purchase totals = $841.24       $899.6336   $899.64   $899.60   $899.80