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 $58.58   6.762%   $62.5412   $62.54   $62.55   $62.50  
  Purchase #2 $150.40   7.648%   $161.9026   $161.90   $161.90   $161.90  
  Purchase #3 $197.31   11.465%   $219.9316   $219.93   $219.95   $219.90  
  Purchase #4 $152.74   13.494%   $173.3507   $173.35   $173.35   $173.40  
  Purchase #5 $55.68   13.263%   $63.0648   $63.06   $63.05   $63.10  
  Purchase #6 $225.89   7.387%   $242.5765   $242.58   $242.60   $242.60  
  Purchase #7 $249.40   8.546%   $270.7137   $270.71   $270.70   $270.70  
  7 purchase totals = $1,090.00       $1,194.0811   $1,194.07   $1,194.10   $1,194.10