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 $92.39   12.852%   $104.264   $104.26   $104.25   $104.30  
  Purchase #2 $61.80   9.390%   $67.603   $67.60   $67.60   $67.60  
  Purchase #3 $139.32   5.721%   $147.2905   $147.29   $147.30   $147.30  
  Purchase #4 $224.60   11.734%   $250.9546   $250.95   $250.95   $251.00  
  Purchase #5 $115.83   7.676%   $124.7211   $124.72   $124.70   $124.70  
  Purchase #6 $242.70   9.430%   $265.5866   $265.59   $265.60   $265.60  
  Purchase #7 $20.65   6.572%   $22.0071   $22.01   $22.00   $22.00  
  7 purchase totals = $897.29       $982.4269   $982.42   $982.40   $982.50