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 $50.88   10.277%   $56.1089   $56.11   $56.10   $56.10  
  Purchase #2 $135.68   9.314%   $148.3172   $148.32   $148.30   $148.30  
  Purchase #3 $168.73   9.681%   $185.0648   $185.06   $185.05   $185.10  
  Purchase #4 $32.83   4.506%   $34.3093   $34.31   $34.30   $34.30  
  Purchase #5 $152.67   9.359%   $166.9584   $166.96   $166.95   $167.00  
  Purchase #6 $124.97   12.683%   $140.8199   $140.82   $140.80   $140.80  
  Purchase #7 $12.79   12.763%   $14.4224   $14.42   $14.40   $14.40  
  7 purchase totals = $678.55       $746.0009   $746.00   $745.90   $746.00