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 $75.35   9.628%   $82.6047   $82.60   $82.60   $82.60  
  Purchase #2 $93.75   11.434%   $104.4694   $104.47   $104.45   $104.50  
  Purchase #3 $147.70   13.440%   $167.5509   $167.55   $167.55   $167.60  
  Purchase #4 $104.83   13.543%   $119.0271   $119.03   $119.05   $119.00  
  Purchase #5 $205.55   10.352%   $226.8285   $226.83   $226.85   $226.80  
  Purchase #6 $185.96   4.290%   $193.9377   $193.94   $193.95   $193.90  
  Purchase #7 $177.96   5.857%   $188.3831   $188.38   $188.40   $188.40  
  7 purchase totals = $991.10       $1,082.8014   $1,082.80   $1,082.85   $1,082.80