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 $60.43   8.636%   $65.6487   $65.65   $65.65   $65.60  
  Purchase #2 $67.68   9.412%   $74.05   $74.05   $74.05   $74.10  
  Purchase #3 $135.33   8.144%   $146.3513   $146.35   $146.35   $146.40  
  Purchase #4 $144.78   11.243%   $161.0576   $161.06   $161.05   $161.10  
  Purchase #5 $127.51   3.119%   $131.487   $131.49   $131.50   $131.50  
  Purchase #6 $236.77   3.568%   $245.218   $245.22   $245.20   $245.20  
  Purchase #7 $77.61   7.259%   $83.2437   $83.24   $83.25   $83.20  
  7 purchase totals = $850.11       $907.0563   $907.06   $907.05   $907.10