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 $84.82   7.612%   $91.2765   $91.28   $91.30   $91.30  
  Purchase #2 $41.88   10.278%   $46.1844   $46.18   $46.20   $46.20  
  Purchase #3 $82.75   13.114%   $93.6018   $93.60   $93.60   $93.60  
  Purchase #4 $106.62   6.192%   $113.2219   $113.22   $113.20   $113.20  
  Purchase #5 $177.46   8.722%   $192.9381   $192.94   $192.95   $192.90  
  Purchase #6 $39.51   3.175%   $40.7644   $40.76   $40.75   $40.80  
  Purchase #7 $216.59   12.831%   $244.3807   $244.38   $244.40   $244.40  
  7 purchase totals = $749.63       $822.3678   $822.36   $822.40   $822.40