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 $126.32   11.829%   $141.2624   $141.26   $141.25   $141.30  
  Purchase #2 $40.27   6.401%   $42.8477   $42.85   $42.85   $42.80  
  Purchase #3 $18.77   13.147%   $21.2377   $21.24   $21.25   $21.20  
  Purchase #4 $242.25   9.397%   $265.0142   $265.01   $265.00   $265.00  
  Purchase #5 $133.45   9.553%   $146.1985   $146.20   $146.20   $146.20  
  Purchase #6 $170.65   12.495%   $191.9727   $191.97   $191.95   $192.00  
  Purchase #7 $191.53   5.447%   $201.9626   $201.96   $201.95   $202.00  
  7 purchase totals = $923.24       $1,010.4958   $1,010.49   $1,010.45   $1,010.50