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 $88.30   6.456%   $94.0006   $94.00   $94.00   $94.00  
  Purchase #2 $129.76   10.144%   $142.9229   $142.92   $142.90   $142.90  
  Purchase #3 $116.54   7.408%   $125.1733   $125.17   $125.15   $125.20  
  Purchase #4 $66.80   10.750%   $73.981   $73.98   $74.00   $74.00  
  Purchase #5 $213.84   10.700%   $236.7209   $236.72   $236.70   $236.70  
  Purchase #6 $215.35   11.238%   $239.551   $239.55   $239.55   $239.60  
  Purchase #7 $231.84   4.578%   $242.4536   $242.45   $242.45   $242.50  
  7 purchase totals = $1,062.43       $1,154.8033   $1,154.79   $1,154.75   $1,154.90