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 $161.37   8.457%   $175.0171   $175.02   $175.00   $175.00  
  Purchase #2 $216.41   7.645%   $232.9545   $232.95   $232.95   $233.00  
  Purchase #3 $125.84   8.745%   $136.8447   $136.84   $136.85   $136.80  
  Purchase #4 $169.60   7.652%   $182.5778   $182.58   $182.60   $182.60  
  Purchase #5 $6.79   10.614%   $7.5107   $7.51   $7.50   $7.50  
  Purchase #6 $172.55   5.367%   $181.8108   $181.81   $181.80   $181.80  
  Purchase #7 $235.27   8.687%   $255.7079   $255.71   $255.70   $255.70  
  7 purchase totals = $1,087.83       $1,172.4235   $1,172.42   $1,172.40   $1,172.40