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 $60.36   3.768%   $62.6344   $62.63   $62.65   $62.60  
  Purchase #2 $203.65   8.610%   $221.1843   $221.18   $221.20   $221.20  
  Purchase #3 $205.31   7.589%   $220.891   $220.89   $220.90   $220.90  
  Purchase #4 $172.30   8.358%   $186.7008   $186.70   $186.70   $186.70  
  Purchase #5 $95.69   6.835%   $102.2304   $102.23   $102.25   $102.20  
  Purchase #6 $250.85   10.117%   $276.2285   $276.23   $276.25   $276.20  
  Purchase #7 $152.52   5.172%   $160.4083   $160.41   $160.40   $160.40  
  7 purchase totals = $1,140.68       $1,230.2777   $1,230.27   $1,230.35   $1,230.20