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 $9.88   10.465%   $10.9139   $10.91   $10.90   $10.90  
  Purchase #2 $20.37   5.635%   $21.5178   $21.52   $21.50   $21.50  
  Purchase #3 $99.76   3.816%   $103.5668   $103.57   $103.55   $103.60  
  Purchase #4 $229.48   7.269%   $246.1609   $246.16   $246.15   $246.20  
  Purchase #5 $184.95   5.147%   $194.4694   $194.47   $194.45   $194.50  
  Purchase #6 $67.42   3.181%   $69.5646   $69.56   $69.55   $69.60  
  Purchase #7 $223.97   3.560%   $231.9433   $231.94   $231.95   $231.90  
  7 purchase totals = $835.83       $878.1367   $878.13   $878.05   $878.20