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 $162.96   11.794%   $182.1795   $182.18   $182.20   $182.20  
  Purchase #2 $190.88   6.202%   $202.7184   $202.72   $202.70   $202.70  
  Purchase #3 $91.67   13.665%   $104.1967   $104.20   $104.20   $104.20  
  Purchase #4 $200.87   4.193%   $209.2925   $209.29   $209.30   $209.30  
  Purchase #5 $39.91   10.580%   $44.1325   $44.13   $44.15   $44.10  
  Purchase #6 $62.29   11.832%   $69.6602   $69.66   $69.65   $69.70  
  Purchase #7 $230.98   13.859%   $262.9915   $262.99   $263.00   $263.00  
  7 purchase totals = $979.56       $1,075.1713   $1,075.17   $1,075.20   $1,075.20