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 $48.57   10.697%   $53.7655   $53.77   $53.75   $53.80  
  Purchase #2 $216.80   13.825%   $246.7726   $246.77   $246.75   $246.80  
  Purchase #3 $249.25   4.455%   $260.3541   $260.35   $260.35   $260.40  
  Purchase #4 $207.81   10.870%   $230.3989   $230.40   $230.40   $230.40  
  Purchase #5 $161.95   9.495%   $177.3272   $177.33   $177.35   $177.30  
  Purchase #6 $232.71   7.413%   $249.9608   $249.96   $249.95   $250.00  
  Purchase #7 $230.58   11.410%   $256.8892   $256.89   $256.90   $256.90  
  7 purchase totals = $1,347.67       $1,475.4683   $1,475.47   $1,475.45   $1,475.60