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 $222.57   6.459%   $236.9458   $236.95   $236.95   $236.90  
  Purchase #2 $112.25   6.631%   $119.6933   $119.69   $119.70   $119.70  
  Purchase #3 $207.52   8.860%   $225.9063   $225.91   $225.90   $225.90  
  Purchase #4 $217.87   10.778%   $241.352   $241.35   $241.35   $241.40  
  Purchase #5 $99.26   10.471%   $109.6535   $109.65   $109.65   $109.70  
  Purchase #6 $107.48   9.459%   $117.6465   $117.65   $117.65   $117.60  
  Purchase #7 $242.56   12.679%   $273.3142   $273.31   $273.30   $273.30  
  7 purchase totals = $1,209.51       $1,324.5116   $1,324.51   $1,324.50   $1,324.50