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 $50.62   6.570%   $53.9457   $53.95   $53.95   $53.90  
  Purchase #2 $54.32   11.641%   $60.6434   $60.64   $60.65   $60.60  
  Purchase #3 $249.86   8.417%   $270.8907   $270.89   $270.90   $270.90  
  Purchase #4 $228.55   3.667%   $236.9309   $236.93   $236.95   $236.90  
  Purchase #5 $144.52   9.809%   $158.696   $158.70   $158.70   $158.70  
  Purchase #6 $199.99   11.659%   $223.3068   $223.31   $223.30   $223.30  
  Purchase #7 $35.43   11.577%   $39.5317   $39.53   $39.55   $39.50  
  7 purchase totals = $963.29       $1,043.9452   $1,043.95   $1,044.00   $1,043.80