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 $47.98   5.710%   $50.7197   $50.72   $50.70   $50.70  
  Purchase #2 $60.83   5.636%   $64.2584   $64.26   $64.25   $64.30  
  Purchase #3 $59.55   4.222%   $62.0642   $62.06   $62.05   $62.10  
  Purchase #4 $215.98   11.786%   $241.4354   $241.44   $241.45   $241.40  
  Purchase #5 $134.56   5.582%   $142.0711   $142.07   $142.05   $142.10  
  Purchase #6 $232.85   11.120%   $258.7429   $258.74   $258.75   $258.70  
  Purchase #7 $61.49   5.329%   $64.7668   $64.77   $64.75   $64.80  
  7 purchase totals = $813.24       $884.0585   $884.06   $884.00   $884.10