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 $249.52   6.535%   $265.8261   $265.83   $265.85   $265.80  
  Purchase #2 $119.47   6.321%   $127.0217   $127.02   $127.00   $127.00  
  Purchase #3 $115.95   9.669%   $127.1612   $127.16   $127.15   $127.20  
  Purchase #4 $232.83   3.279%   $240.4645   $240.46   $240.45   $240.50  
  Purchase #5 $81.93   3.456%   $84.7615   $84.76   $84.75   $84.80  
  Purchase #6 $177.89   7.200%   $190.6981   $190.70   $190.70   $190.70  
  Purchase #7 $14.90   5.618%   $15.7371   $15.74   $15.75   $15.70  
  7 purchase totals = $992.49       $1,051.6702   $1,051.67   $1,051.65   $1,051.70