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 $178.25   12.166%   $199.9359   $199.94   $199.95   $199.90  
  Purchase #2 $120.62   9.726%   $132.3515   $132.35   $132.35   $132.40  
  Purchase #3 $35.37   7.573%   $38.0486   $38.05   $38.05   $38.00  
  Purchase #4 $168.39   9.432%   $184.2725   $184.27   $184.25   $184.30  
  Purchase #5 $80.83   9.369%   $88.403   $88.40   $88.40   $88.40  
  Purchase #6 $128.53   3.190%   $132.6301   $132.63   $132.65   $132.60  
  Purchase #7 $65.66   10.209%   $72.3632   $72.36   $72.35   $72.40  
  7 purchase totals = $777.65       $848.0048   $848.00   $848.00   $848.00