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 $184.32   6.136%   $195.6299   $195.63   $195.65   $195.60  
  Purchase #2 $87.62   10.746%   $97.0356   $97.04   $97.05   $97.00  
  Purchase #3 $159.30   6.821%   $170.1659   $170.17   $170.15   $170.20  
  Purchase #4 $237.69   11.602%   $265.2668   $265.27   $265.25   $265.30  
  Purchase #5 $6.68   12.364%   $7.5059   $7.51   $7.50   $7.50  
  Purchase #6 $183.70   8.621%   $199.5368   $199.54   $199.55   $199.50  
  Purchase #7 $33.37   9.685%   $36.6019   $36.60   $36.60   $36.60  
  7 purchase totals = $892.68       $971.7428   $971.76   $971.75   $971.70