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 $138.97   5.494%   $146.605   $146.61   $146.60   $146.60  
  Purchase #2 $112.51   4.839%   $117.9544   $117.95   $117.95   $118.00  
  Purchase #3 $192.79   9.219%   $210.5633   $210.56   $210.55   $210.60  
  Purchase #4 $88.49   8.187%   $95.7347   $95.73   $95.75   $95.70  
  Purchase #5 $36.38   4.286%   $37.9392   $37.94   $37.95   $37.90  
  Purchase #6 $217.68   4.361%   $227.173   $227.17   $227.15   $227.20  
  Purchase #7 $176.42   13.174%   $199.6616   $199.66   $199.65   $199.70  
  7 purchase totals = $963.24       $1,035.6312   $1,035.62   $1,035.60   $1,035.70