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 $189.95   6.843%   $202.9483   $202.95   $202.95   $202.90  
  Purchase #2 $67.55   6.410%   $71.88   $71.88   $71.90   $71.90  
  Purchase #3 $165.32   5.527%   $174.4572   $174.46   $174.45   $174.50  
  Purchase #4 $75.56   3.653%   $78.3202   $78.32   $78.30   $78.30  
  Purchase #5 $16.41   9.120%   $17.9066   $17.91   $17.90   $17.90  
  Purchase #6 $131.45   6.279%   $139.7037   $139.70   $139.70   $139.70  
  Purchase #7 $48.40   4.821%   $50.7334   $50.73   $50.75   $50.70  
  7 purchase totals = $694.64       $735.9494   $735.95   $735.95   $735.90