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 $56.47   10.841%   $62.5919   $62.59   $62.60   $62.60  
  Purchase #2 $97.70   12.843%   $110.2476   $110.25   $110.25   $110.20  
  Purchase #3 $218.30   6.137%   $231.6971   $231.70   $231.70   $231.70  
  Purchase #4 $239.71   3.142%   $247.2417   $247.24   $247.25   $247.20  
  Purchase #5 $127.40   3.630%   $132.0246   $132.02   $132.00   $132.00  
  Purchase #6 $23.98   13.819%   $27.2938   $27.29   $27.30   $27.30  
  Purchase #7 $12.88   8.281%   $13.9466   $13.95   $13.95   $13.90  
  7 purchase totals = $776.44       $825.0433   $825.04   $825.05   $824.90