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 $106.66   10.624%   $117.9916   $117.99   $118.00   $118.00  
  Purchase #2 $52.64   12.116%   $59.0179   $59.02   $59.00   $59.00  
  Purchase #3 $220.53   5.148%   $231.8829   $231.88   $231.90   $231.90  
  Purchase #4 $85.53   11.277%   $95.1752   $95.18   $95.20   $95.20  
  Purchase #5 $11.98   9.557%   $13.1249   $13.12   $13.10   $13.10  
  Purchase #6 $233.64   10.718%   $258.6815   $258.68   $258.70   $258.70  
  Purchase #7 $192.73   13.215%   $218.1993   $218.20   $218.20   $218.20  
  7 purchase totals = $903.71       $994.0733   $994.07   $994.10   $994.10