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 $168.78   3.202%   $174.1843   $174.18   $174.20   $174.20  
  Purchase #2 $105.63   11.409%   $117.6813   $117.68   $117.70   $117.70  
  Purchase #3 $157.64   13.312%   $178.625   $178.63   $178.65   $178.60  
  Purchase #4 $106.52   3.123%   $109.8466   $109.85   $109.85   $109.80  
  Purchase #5 $151.27   10.319%   $166.8796   $166.88   $166.90   $166.90  
  Purchase #6 $190.43   12.764%   $214.7365   $214.74   $214.75   $214.70  
  Purchase #7 $21.39   8.367%   $23.1797   $23.18   $23.20   $23.20  
  7 purchase totals = $901.66       $985.1330   $985.14   $985.25   $985.10