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 $59.53   5.346%   $62.7125   $62.71   $62.70   $62.70  
  Purchase #2 $91.28   3.866%   $94.8089   $94.81   $94.80   $94.80  
  Purchase #3 $104.40   10.868%   $115.7462   $115.75   $115.75   $115.70  
  Purchase #4 $249.69   7.715%   $268.9536   $268.95   $268.95   $269.00  
  Purchase #5 $135.89   7.574%   $146.1823   $146.18   $146.20   $146.20  
  Purchase #6 $85.66   6.634%   $91.3427   $91.34   $91.35   $91.30  
  Purchase #7 $81.98   12.186%   $91.9701   $91.97   $91.95   $92.00  
  7 purchase totals = $808.43       $871.7163   $871.71   $871.70   $871.70