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 $107.42   8.548%   $116.6023   $116.60   $116.60   $116.60  
  Purchase #2 $57.81   9.333%   $63.2054   $63.21   $63.20   $63.20  
  Purchase #3 $156.27   8.333%   $169.292   $169.29   $169.30   $169.30  
  Purchase #4 $82.54   8.113%   $89.2365   $89.24   $89.25   $89.20  
  Purchase #5 $18.94   10.165%   $20.8653   $20.87   $20.85   $20.90  
  Purchase #6 $154.33   4.761%   $161.6777   $161.68   $161.70   $161.70  
  Purchase #7 $128.51   7.863%   $138.6147   $138.61   $138.60   $138.60  
  7 purchase totals = $705.82       $759.4939   $759.50   $759.50   $759.50