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 $168.81   4.483%   $176.3778   $176.38   $176.40   $176.40  
  Purchase #2 $137.62   10.184%   $151.6352   $151.64   $151.65   $151.60  
  Purchase #3 $25.36   13.517%   $28.7879   $28.79   $28.80   $28.80  
  Purchase #4 $85.83   6.779%   $91.6484   $91.65   $91.65   $91.60  
  Purchase #5 $130.81   5.664%   $138.2191   $138.22   $138.20   $138.20  
  Purchase #6 $231.64   6.554%   $246.8217   $246.82   $246.80   $246.80  
  Purchase #7 $142.51   12.810%   $160.7655   $160.77   $160.75   $160.80  
  7 purchase totals = $922.58       $994.2556   $994.27   $994.25   $994.20