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 $24.58   9.214%   $26.8448   $26.84   $26.85   $26.80  
  Purchase #2 $41.65   10.663%   $46.0911   $46.09   $46.10   $46.10  
  Purchase #3 $81.88   12.184%   $91.8563   $91.86   $91.85   $91.90  
  Purchase #4 $93.82   11.310%   $104.431   $104.43   $104.45   $104.40  
  Purchase #5 $244.34   10.231%   $269.3384   $269.34   $269.35   $269.30  
  Purchase #6 $217.92   10.530%   $240.867   $240.87   $240.85   $240.90  
  Purchase #7 $157.28   3.211%   $162.3303   $162.33   $162.35   $162.30  
  7 purchase totals = $861.47       $941.7589   $941.76   $941.80   $941.70