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 $211.38   11.736%   $236.1876   $236.19   $236.20   $236.20  
  Purchase #2 $212.57   9.291%   $232.3199   $232.32   $232.30   $232.30  
  Purchase #3 $31.44   4.368%   $32.8133   $32.81   $32.80   $32.80  
  Purchase #4 $235.92   9.673%   $258.7405   $258.74   $258.75   $258.70  
  Purchase #5 $208.53   8.343%   $225.9277   $225.93   $225.95   $225.90  
  Purchase #6 $233.26   4.804%   $244.4658   $244.47   $244.45   $244.50  
  Purchase #7 $126.69   13.205%   $143.4194   $143.42   $143.40   $143.40  
  7 purchase totals = $1,259.79       $1,373.8742   $1,373.88   $1,373.85   $1,373.80