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 $34.28   6.764%   $36.5987   $36.60   $36.60   $36.60  
  Purchase #2 $229.90   11.331%   $255.95   $255.95   $255.95   $256.00  
  Purchase #3 $138.83   5.673%   $146.7058   $146.71   $146.70   $146.70  
  Purchase #4 $111.25   8.111%   $120.2735   $120.27   $120.25   $120.30  
  Purchase #5 $171.80   6.708%   $183.3243   $183.32   $183.30   $183.30  
  Purchase #6 $24.46   12.839%   $27.6004   $27.60   $27.60   $27.60  
  Purchase #7 $170.27   3.852%   $176.8288   $176.83   $176.85   $176.80  
  7 purchase totals = $880.79       $947.2815   $947.28   $947.25   $947.30