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 $54.57   12.443%   $61.3601   $61.36   $61.35   $61.40  
  Purchase #2 $150.72   4.588%   $157.635   $157.64   $157.65   $157.60  
  Purchase #3 $191.79   12.347%   $215.4703   $215.47   $215.45   $215.50  
  Purchase #4 $140.75   9.240%   $153.7553   $153.76   $153.75   $153.80  
  Purchase #5 $41.82   6.481%   $44.5304   $44.53   $44.55   $44.50  
  Purchase #6 $66.37   11.375%   $73.9196   $73.92   $73.90   $73.90  
  Purchase #7 $76.56   12.311%   $85.9853   $85.99   $86.00   $86.00  
  7 purchase totals = $722.58       $792.6560   $792.67   $792.65   $792.70