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 $201.72   11.496%   $224.9097   $224.91   $224.90   $224.90  
  Purchase #2 $12.64   11.784%   $14.1295   $14.13   $14.15   $14.10  
  Purchase #3 $44.55   9.215%   $48.6553   $48.66   $48.65   $48.70  
  Purchase #4 $185.91   10.794%   $205.9771   $205.98   $206.00   $206.00  
  Purchase #5 $82.34   12.337%   $92.4983   $92.50   $92.50   $92.50  
  Purchase #6 $242.83   5.244%   $255.564   $255.56   $255.55   $255.60  
  Purchase #7 $226.79   12.145%   $254.3336   $254.33   $254.35   $254.30  
  7 purchase totals = $996.78       $1,096.0675   $1,096.07   $1,096.10   $1,096.10