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 $205.36   11.206%   $228.3726   $228.37   $228.35   $228.40  
  Purchase #2 $36.51   4.358%   $38.1011   $38.10   $38.10   $38.10  
  Purchase #3 $24.50   4.208%   $25.531   $25.53   $25.55   $25.50  
  Purchase #4 $56.88   12.527%   $64.0054   $64.01   $64.00   $64.00  
  Purchase #5 $215.87   9.332%   $236.015   $236.02   $236.00   $236.00  
  Purchase #6 $110.96   7.276%   $119.0334   $119.03   $119.05   $119.00  
  Purchase #7 $55.35   6.303%   $58.8387   $58.84   $58.85   $58.80  
  7 purchase totals = $705.43       $769.8972   $769.90   $769.90   $769.80