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 $218.93   10.783%   $242.5372   $242.54   $242.55   $242.50  
  Purchase #2 $59.96   4.533%   $62.678   $62.68   $62.70   $62.70  
  Purchase #3 $192.33   7.622%   $206.9894   $206.99   $207.00   $207.00  
  Purchase #4 $117.75   6.183%   $125.0305   $125.03   $125.05   $125.00  
  Purchase #5 $124.59   11.734%   $139.2094   $139.21   $139.20   $139.20  
  Purchase #6 $54.78   10.417%   $60.4864   $60.49   $60.50   $60.50  
  Purchase #7 $219.26   11.212%   $243.8434   $243.84   $243.85   $243.80  
  7 purchase totals = $987.60       $1,080.7743   $1,080.78   $1,080.85   $1,080.70