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 $211.98   5.534%   $223.711   $223.71   $223.70   $223.70  
  Purchase #2 $54.84   12.385%   $61.6319   $61.63   $61.65   $61.60  
  Purchase #3 $47.41   7.583%   $51.0051   $51.01   $51.00   $51.00  
  Purchase #4 $47.80   13.658%   $54.3285   $54.33   $54.35   $54.30  
  Purchase #5 $185.60   5.516%   $195.8377   $195.84   $195.85   $195.80  
  Purchase #6 $120.45   9.778%   $132.2276   $132.23   $132.25   $132.20  
  Purchase #7 $193.43   11.713%   $216.0865   $216.09   $216.10   $216.10  
  7 purchase totals = $861.51       $934.8283   $934.84   $934.90   $934.70