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 $129.55   9.548%   $141.9194   $141.92   $141.90   $141.90  
  Purchase #2 $66.69   7.205%   $71.495   $71.50   $71.50   $71.50  
  Purchase #3 $196.33   4.217%   $204.6092   $204.61   $204.60   $204.60  
  Purchase #4 $117.61   3.216%   $121.3923   $121.39   $121.40   $121.40  
  Purchase #5 $208.27   8.771%   $226.5374   $226.54   $226.55   $226.50  
  Purchase #6 $160.32   5.572%   $169.253   $169.25   $169.25   $169.30  
  Purchase #7 $85.65   13.311%   $97.0509   $97.05   $97.05   $97.10  
  7 purchase totals = $964.42       $1,032.2572   $1,032.26   $1,032.25   $1,032.30