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 $69.71   9.318%   $76.2056   $76.21   $76.20   $76.20  
  Purchase #2 $26.59   5.548%   $28.0652   $28.07   $28.05   $28.10  
  Purchase #3 $145.80   5.482%   $153.7928   $153.79   $153.80   $153.80  
  Purchase #4 $59.61   4.659%   $62.3872   $62.39   $62.40   $62.40  
  Purchase #5 $227.82   10.356%   $251.413   $251.41   $251.40   $251.40  
  Purchase #6 $44.40   12.459%   $49.9318   $49.93   $49.95   $49.90  
  Purchase #7 $212.66   13.334%   $241.0161   $241.02   $241.00   $241.00  
  7 purchase totals = $786.59       $862.8117   $862.82   $862.80   $862.80