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 $245.43   12.459%   $276.0081   $276.01   $276.00   $276.00  
  Purchase #2 $132.55   13.355%   $150.2521   $150.25   $150.25   $150.30  
  Purchase #3 $249.78   4.788%   $261.7395   $261.74   $261.75   $261.70  
  Purchase #4 $49.65   10.821%   $55.0226   $55.02   $55.00   $55.00  
  Purchase #5 $150.49   6.689%   $160.5563   $160.56   $160.55   $160.60  
  Purchase #6 $212.76   5.651%   $224.7831   $224.78   $224.80   $224.80  
  Purchase #7 $201.33   12.147%   $225.7856   $225.79   $225.80   $225.80  
  7 purchase totals = $1,241.99       $1,354.1473   $1,354.15   $1,354.15   $1,354.20