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 $174.89   4.648%   $183.0189   $183.02   $183.00   $183.00  
  Purchase #2 $141.50   9.848%   $155.4349   $155.43   $155.45   $155.40  
  Purchase #3 $211.99   13.477%   $240.5599   $240.56   $240.55   $240.60  
  Purchase #4 $248.76   4.595%   $260.1905   $260.19   $260.20   $260.20  
  Purchase #5 $63.88   8.781%   $69.4893   $69.49   $69.50   $69.50  
  Purchase #6 $163.76   6.565%   $174.5108   $174.51   $174.50   $174.50  
  Purchase #7 $57.63   6.313%   $61.2682   $61.27   $61.25   $61.30  
  7 purchase totals = $1,062.41       $1,144.4725   $1,144.47   $1,144.45   $1,144.50