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 $86.46   13.356%   $98.0076   $98.01   $98.00   $98.00  
  Purchase #2 $49.54   13.423%   $56.1898   $56.19   $56.20   $56.20  
  Purchase #3 $44.88   6.260%   $47.6895   $47.69   $47.70   $47.70  
  Purchase #4 $112.70   8.585%   $122.3753   $122.38   $122.40   $122.40  
  Purchase #5 $160.75   7.400%   $172.6455   $172.65   $172.65   $172.60  
  Purchase #6 $141.88   13.479%   $161.004   $161.00   $161.00   $161.00  
  Purchase #7 $209.30   6.433%   $222.7643   $222.76   $222.75   $222.80  
  7 purchase totals = $805.51       $880.6760   $880.68   $880.70   $880.70