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 $61.26   5.546%   $64.6575   $64.66   $64.65   $64.70  
  Purchase #2 $212.75   9.304%   $232.5443   $232.54   $232.55   $232.50  
  Purchase #3 $46.60   5.145%   $48.9976   $49.00   $49.00   $49.00  
  Purchase #4 $126.85   5.603%   $133.9574   $133.96   $133.95   $134.00  
  Purchase #5 $15.33   12.589%   $17.2599   $17.26   $17.25   $17.30  
  Purchase #6 $152.64   13.833%   $173.7547   $173.75   $173.75   $173.80  
  Purchase #7 $124.91   8.155%   $135.0964   $135.10   $135.10   $135.10  
  7 purchase totals = $740.34       $806.2678   $806.27   $806.25   $806.40