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 $22.94   10.699%   $25.3944   $25.39   $25.40   $25.40  
  Purchase #2 $137.89   8.481%   $149.5845   $149.58   $149.60   $149.60  
  Purchase #3 $52.67   10.667%   $58.2883   $58.29   $58.30   $58.30  
  Purchase #4 $61.28   7.201%   $65.6928   $65.69   $65.70   $65.70  
  Purchase #5 $133.79   7.178%   $143.3934   $143.39   $143.40   $143.40  
  Purchase #6 $240.32   9.622%   $263.4436   $263.44   $263.45   $263.40  
  Purchase #7 $137.68   9.302%   $150.487   $150.49   $150.50   $150.50  
  7 purchase totals = $786.57       $856.2840   $856.27   $856.35   $856.30