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 $46.63   13.104%   $52.7404   $52.74   $52.75   $52.70  
  Purchase #2 $71.45   8.581%   $77.5811   $77.58   $77.60   $77.60  
  Purchase #3 $66.37   12.842%   $74.8932   $74.89   $74.90   $74.90  
  Purchase #4 $88.51   12.317%   $99.4118   $99.41   $99.40   $99.40  
  Purchase #5 $210.66   9.219%   $230.0807   $230.08   $230.10   $230.10  
  Purchase #6 $102.64   11.590%   $114.536   $114.54   $114.55   $114.50  
  Purchase #7 $198.74   3.767%   $206.2265   $206.23   $206.25   $206.20  
  7 purchase totals = $785.00       $855.4697   $855.47   $855.55   $855.40