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 $54.87   5.714%   $58.0053   $58.01   $58.00   $58.00  
  Purchase #2 $238.54   3.852%   $247.7286   $247.73   $247.75   $247.70  
  Purchase #3 $63.50   5.855%   $67.2179   $67.22   $67.20   $67.20  
  Purchase #4 $226.35   3.427%   $234.107   $234.11   $234.10   $234.10  
  Purchase #5 $135.64   5.543%   $143.1585   $143.16   $143.15   $143.20  
  Purchase #6 $119.53   10.758%   $132.389   $132.39   $132.40   $132.40  
  Purchase #7 $82.84   8.355%   $89.7613   $89.76   $89.75   $89.80  
  7 purchase totals = $921.27       $972.3676   $972.38   $972.35   $972.40