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 $60.80   3.516%   $62.9377   $62.94   $62.95   $62.90  
  Purchase #2 $64.43   5.807%   $68.1715   $68.17   $68.15   $68.20  
  Purchase #3 $45.57   8.138%   $49.2785   $49.28   $49.30   $49.30  
  Purchase #4 $76.67   6.375%   $81.5577   $81.56   $81.55   $81.60  
  Purchase #5 $32.56   11.442%   $36.2855   $36.29   $36.30   $36.30  
  Purchase #6 $32.63   7.133%   $34.9575   $34.96   $34.95   $35.00  
  Purchase #7 $184.55   9.753%   $202.5492   $202.55   $202.55   $202.50  
  7 purchase totals = $497.21       $535.7376   $535.75   $535.75   $535.80