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 $105.78   13.403%   $119.9577   $119.96   $119.95   $120.00  
  Purchase #2 $95.47   7.621%   $102.7458   $102.75   $102.75   $102.70  
  Purchase #3 $176.53   12.700%   $198.9493   $198.95   $198.95   $198.90  
  Purchase #4 $49.26   12.703%   $55.5175   $55.52   $55.50   $55.50  
  Purchase #5 $34.73   9.862%   $38.1551   $38.16   $38.15   $38.20  
  Purchase #6 $107.94   6.152%   $114.5805   $114.58   $114.60   $114.60  
  Purchase #7 $124.25   9.613%   $136.1942   $136.19   $136.20   $136.20  
  7 purchase totals = $693.96       $766.1001   $766.11   $766.10   $766.10