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 $63.31   7.467%   $68.0374   $68.04   $68.05   $68.00  
  Purchase #2 $180.25   6.637%   $192.2132   $192.21   $192.20   $192.20  
  Purchase #3 $126.64   11.637%   $141.3771   $141.38   $141.40   $141.40  
  Purchase #4 $160.63   5.596%   $169.6189   $169.62   $169.60   $169.60  
  Purchase #5 $64.49   6.398%   $68.6161   $68.62   $68.60   $68.60  
  Purchase #6 $99.96   6.486%   $106.4434   $106.44   $106.45   $106.40  
  Purchase #7 $65.54   8.255%   $70.9503   $70.95   $70.95   $71.00  
  7 purchase totals = $760.82       $817.2564   $817.26   $817.25   $817.20