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 $54.60   3.404%   $56.4586   $56.46   $56.45   $56.50  
  Purchase #2 $119.47   13.331%   $135.3965   $135.40   $135.40   $135.40  
  Purchase #3 $190.79   12.151%   $213.9729   $213.97   $213.95   $214.00  
  Purchase #4 $26.41   11.765%   $29.5171   $29.52   $29.50   $29.50  
  Purchase #5 $249.81   11.843%   $279.395   $279.40   $279.40   $279.40  
  Purchase #6 $199.89   7.134%   $214.1502   $214.15   $214.15   $214.20  
  Purchase #7 $232.98   13.625%   $264.7235   $264.72   $264.70   $264.70  
  7 purchase totals = $1,073.95       $1,193.6138   $1,193.62   $1,193.55   $1,193.70