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 $230.39   6.110%   $244.4668   $244.47   $244.45   $244.50  
  Purchase #2 $158.31   11.623%   $176.7104   $176.71   $176.70   $176.70  
  Purchase #3 $107.59   10.151%   $118.5115   $118.51   $118.50   $118.50  
  Purchase #4 $74.37   4.387%   $77.6326   $77.63   $77.65   $77.60  
  Purchase #5 $225.93   11.821%   $252.6372   $252.64   $252.65   $252.60  
  Purchase #6 $120.40   4.486%   $125.8011   $125.80   $125.80   $125.80  
  Purchase #7 $36.31   3.179%   $37.4643   $37.46   $37.45   $37.50  
  7 purchase totals = $953.30       $1,033.2239   $1,033.22   $1,033.20   $1,033.20