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 $52.53   11.863%   $58.7616   $58.76   $58.75   $58.80  
  Purchase #2 $125.67   11.602%   $140.2502   $140.25   $140.25   $140.30  
  Purchase #3 $58.30   6.166%   $61.8948   $61.89   $61.90   $61.90  
  Purchase #4 $80.71   6.438%   $85.9061   $85.91   $85.90   $85.90  
  Purchase #5 $26.86   10.453%   $29.6677   $29.67   $29.65   $29.70  
  Purchase #6 $133.35   11.812%   $149.1013   $149.10   $149.10   $149.10  
  Purchase #7 $205.99   12.424%   $231.5822   $231.58   $231.60   $231.60  
  7 purchase totals = $683.41       $757.1639   $757.16   $757.15   $757.30