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 $189.61   7.595%   $204.0109   $204.01   $204.00   $204.00  
  Purchase #2 $154.98   13.148%   $175.3568   $175.36   $175.35   $175.40  
  Purchase #3 $110.62   11.667%   $123.526   $123.53   $123.55   $123.50  
  Purchase #4 $30.85   5.797%   $32.6384   $32.64   $32.65   $32.60  
  Purchase #5 $129.41   13.204%   $146.4973   $146.50   $146.50   $146.50  
  Purchase #6 $21.73   11.184%   $24.1603   $24.16   $24.15   $24.20  
  Purchase #7 $193.49   10.230%   $213.284   $213.28   $213.30   $213.30  
  7 purchase totals = $830.69       $919.4737   $919.48   $919.50   $919.50