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 $239.65   11.756%   $267.8233   $267.82   $267.80   $267.80  
  Purchase #2 $182.91   12.659%   $206.0646   $206.06   $206.05   $206.10  
  Purchase #3 $194.46   4.695%   $203.5899   $203.59   $203.60   $203.60  
  Purchase #4 $209.50   11.844%   $234.3132   $234.31   $234.30   $234.30  
  Purchase #5 $109.79   10.746%   $121.588   $121.59   $121.60   $121.60  
  Purchase #6 $220.46   13.547%   $250.3257   $250.33   $250.35   $250.30  
  Purchase #7 $76.71   7.372%   $82.3651   $82.37   $82.35   $82.40  
  7 purchase totals = $1,233.48       $1,366.0698   $1,366.07   $1,366.05   $1,366.10