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 $42.46   5.542%   $44.8131   $44.81   $44.80   $44.80  
  Purchase #2 $213.67   5.829%   $226.1248   $226.12   $226.10   $226.10  
  Purchase #3 $199.76   5.225%   $210.1975   $210.20   $210.20   $210.20  
  Purchase #4 $205.25   5.432%   $216.3992   $216.40   $216.40   $216.40  
  Purchase #5 $66.34   12.135%   $74.3904   $74.39   $74.40   $74.40  
  Purchase #6 $187.62   13.725%   $213.3708   $213.37   $213.35   $213.40  
  Purchase #7 $250.88   6.151%   $266.3116   $266.31   $266.30   $266.30  
  7 purchase totals = $1,165.98       $1,251.6074   $1,251.60   $1,251.55   $1,251.60