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 $55.55   6.848%   $59.3541   $59.35   $59.35   $59.40  
  Purchase #2 $113.99   9.754%   $125.1086   $125.11   $125.10   $125.10  
  Purchase #3 $58.60   9.253%   $64.0223   $64.02   $64.00   $64.00  
  Purchase #4 $168.25   9.132%   $183.6146   $183.61   $183.60   $183.60  
  Purchase #5 $151.78   11.234%   $168.831   $168.83   $168.85   $168.80  
  Purchase #6 $173.77   13.605%   $197.4114   $197.41   $197.40   $197.40  
  Purchase #7 $33.71   7.446%   $36.22   $36.22   $36.20   $36.20  
  7 purchase totals = $755.65       $834.5620   $834.55   $834.50   $834.50