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 $111.34   13.569%   $126.4477   $126.45   $126.45   $126.40  
  Purchase #2 $64.61   10.403%   $71.3314   $71.33   $71.35   $71.30  
  Purchase #3 $246.75   11.676%   $275.5605   $275.56   $275.55   $275.60  
  Purchase #4 $121.90   11.354%   $135.7405   $135.74   $135.75   $135.70  
  Purchase #5 $133.51   3.309%   $137.9278   $137.93   $137.95   $137.90  
  Purchase #6 $87.84   3.692%   $91.0831   $91.08   $91.10   $91.10  
  Purchase #7 $32.81   13.313%   $37.178   $37.18   $37.20   $37.20  
  7 purchase totals = $798.76       $875.2690   $875.27   $875.35   $875.20