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 $9.81   11.584%   $10.9464   $10.95   $10.95   $10.90  
  Purchase #2 $162.32   8.813%   $176.6253   $176.63   $176.65   $176.60  
  Purchase #3 $33.98   12.125%   $38.1001   $38.10   $38.10   $38.10  
  Purchase #4 $180.46   7.134%   $193.334   $193.33   $193.35   $193.30  
  Purchase #5 $217.29   10.618%   $240.3619   $240.36   $240.35   $240.40  
  Purchase #6 $84.44   10.817%   $93.5739   $93.57   $93.55   $93.60  
  Purchase #7 $172.58   6.145%   $183.185   $183.19   $183.20   $183.20  
  7 purchase totals = $860.88       $936.1266   $936.13   $936.15   $936.10