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 $50.68   13.630%   $57.5877   $57.59   $57.60   $57.60  
  Purchase #2 $147.51   7.104%   $157.9891   $157.99   $158.00   $158.00  
  Purchase #3 $115.93   11.331%   $129.066   $129.07   $129.05   $129.10  
  Purchase #4 $62.35   4.235%   $64.9905   $64.99   $65.00   $65.00  
  Purchase #5 $106.28   13.576%   $120.7086   $120.71   $120.70   $120.70  
  Purchase #6 $185.59   9.622%   $203.4475   $203.45   $203.45   $203.40  
  Purchase #7 $201.79   3.632%   $209.119   $209.12   $209.10   $209.10  
  7 purchase totals = $870.13       $942.9084   $942.92   $942.90   $942.90