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 $225.54   3.597%   $233.6527   $233.65   $233.65   $233.70  
  Purchase #2 $132.29   9.116%   $144.3496   $144.35   $144.35   $144.30  
  Purchase #3 $218.56   3.366%   $225.9167   $225.92   $225.90   $225.90  
  Purchase #4 $88.62   9.715%   $97.2294   $97.23   $97.25   $97.20  
  Purchase #5 $148.92   10.138%   $164.0175   $164.02   $164.00   $164.00  
  Purchase #6 $59.53   3.769%   $61.7737   $61.77   $61.75   $61.80  
  Purchase #7 $150.86   11.851%   $168.7384   $168.74   $168.75   $168.70  
  7 purchase totals = $1,024.32       $1,095.6780   $1,095.68   $1,095.65   $1,095.60