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 $20.52   6.852%   $21.926   $21.93   $21.95   $21.90  
  Purchase #2 $143.72   13.596%   $163.2602   $163.26   $163.25   $163.30  
  Purchase #3 $225.61   12.242%   $253.2292   $253.23   $253.25   $253.20  
  Purchase #4 $201.90   10.803%   $223.7113   $223.71   $223.70   $223.70  
  Purchase #5 $39.34   7.530%   $42.3023   $42.30   $42.30   $42.30  
  Purchase #6 $30.63   13.549%   $34.7801   $34.78   $34.80   $34.80  
  Purchase #7 $224.72   3.671%   $232.9695   $232.97   $232.95   $233.00  
  7 purchase totals = $886.44       $972.1786   $972.18   $972.20   $972.20