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 $93.94   10.570%   $103.8695   $103.87   $103.85   $103.90  
  Purchase #2 $176.42   9.185%   $192.6242   $192.62   $192.60   $192.60  
  Purchase #3 $75.39   8.860%   $82.0696   $82.07   $82.05   $82.10  
  Purchase #4 $108.42   5.359%   $114.2302   $114.23   $114.25   $114.20  
  Purchase #5 $172.98   11.632%   $193.101   $193.10   $193.10   $193.10  
  Purchase #6 $48.95   11.393%   $54.5269   $54.53   $54.55   $54.50  
  Purchase #7 $212.55   7.268%   $227.9981   $228.00   $228.00   $228.00  
  7 purchase totals = $888.65       $968.4195   $968.42   $968.40   $968.40