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 $169.43   10.652%   $187.4777   $187.48   $187.50   $187.50  
  Purchase #2 $41.34   11.781%   $46.2103   $46.21   $46.20   $46.20  
  Purchase #3 $51.94   6.826%   $55.4854   $55.49   $55.50   $55.50  
  Purchase #4 $49.58   6.469%   $52.7873   $52.79   $52.80   $52.80  
  Purchase #5 $114.84   6.749%   $122.5906   $122.59   $122.60   $122.60  
  Purchase #6 $131.65   3.528%   $136.2946   $136.29   $136.30   $136.30  
  Purchase #7 $150.45   10.394%   $166.0878   $166.09   $166.10   $166.10  
  7 purchase totals = $709.23       $766.9337   $766.94   $767.00   $767.00