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 $208.34   12.532%   $234.4492   $234.45   $234.45   $234.40  
  Purchase #2 $159.34   6.103%   $169.0645   $169.06   $169.05   $169.10  
  Purchase #3 $117.71   5.571%   $124.2676   $124.27   $124.25   $124.30  
  Purchase #4 $88.92   7.191%   $95.3142   $95.31   $95.30   $95.30  
  Purchase #5 $201.26   3.414%   $208.131   $208.13   $208.15   $208.10  
  Purchase #6 $152.76   5.641%   $161.3772   $161.38   $161.40   $161.40  
  Purchase #7 $37.94   3.783%   $39.3753   $39.38   $39.40   $39.40  
  7 purchase totals = $966.27       $1,031.9790   $1,031.98   $1,032.00   $1,032.00