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 $169.76   8.172%   $183.6328   $183.63   $183.65   $183.60  
  Purchase #2 $29.48   11.172%   $32.7735   $32.77   $32.75   $32.80  
  Purchase #3 $92.47   8.426%   $100.2615   $100.26   $100.25   $100.30  
  Purchase #4 $126.83   8.273%   $137.3226   $137.32   $137.30   $137.30  
  Purchase #5 $119.74   12.584%   $134.8081   $134.81   $134.80   $134.80  
  Purchase #6 $244.71   11.432%   $272.6852   $272.69   $272.70   $272.70  
  Purchase #7 $147.27   8.302%   $159.4964   $159.50   $159.50   $159.50  
  7 purchase totals = $930.26       $1,020.9801   $1,020.98   $1,020.95   $1,021.00