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 $126.33   5.697%   $133.527   $133.53   $133.55   $133.50  
  Purchase #2 $59.75   6.469%   $63.6152   $63.62   $63.60   $63.60  
  Purchase #3 $70.97   6.508%   $75.5887   $75.59   $75.60   $75.60  
  Purchase #4 $213.78   10.221%   $235.6305   $235.63   $235.65   $235.60  
  Purchase #5 $151.30   5.565%   $159.7198   $159.72   $159.70   $159.70  
  Purchase #6 $238.53   12.324%   $267.9264   $267.93   $267.95   $267.90  
  Purchase #7 $205.85   3.794%   $213.6599   $213.66   $213.65   $213.70  
  7 purchase totals = $1,066.51       $1,149.6675   $1,149.68   $1,149.70   $1,149.60