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 $90.86   4.474%   $94.9251   $94.93   $94.95   $94.90  
  Purchase #2 $108.72   7.224%   $116.5739   $116.57   $116.55   $116.60  
  Purchase #3 $54.99   4.168%   $57.282   $57.28   $57.30   $57.30  
  Purchase #4 $104.60   13.792%   $119.0264   $119.03   $119.05   $119.00  
  Purchase #5 $161.26   6.202%   $171.2613   $171.26   $171.25   $171.30  
  Purchase #6 $151.61   13.565%   $172.1759   $172.18   $172.20   $172.20  
  Purchase #7 $173.72   6.340%   $184.7338   $184.73   $184.75   $184.70  
  7 purchase totals = $845.76       $915.9784   $915.98   $916.05   $916.00