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 $23.66   6.739%   $25.2544   $25.25   $25.25   $25.30  
  Purchase #2 $150.82   11.151%   $167.6379   $167.64   $167.65   $167.60  
  Purchase #3 $86.45   6.281%   $91.8799   $91.88   $91.90   $91.90  
  Purchase #4 $29.78   7.676%   $32.0659   $32.07   $32.05   $32.10  
  Purchase #5 $212.30   7.729%   $228.7087   $228.71   $228.70   $228.70  
  Purchase #6 $94.67   8.194%   $102.4273   $102.43   $102.45   $102.40  
  Purchase #7 $91.38   7.579%   $98.3057   $98.31   $98.30   $98.30  
  7 purchase totals = $689.06       $746.2798   $746.29   $746.30   $746.30