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 $228.29   7.870%   $246.2564   $246.26   $246.25   $246.30  
  Purchase #2 $88.86   11.832%   $99.3739   $99.37   $99.35   $99.40  
  Purchase #3 $183.55   5.691%   $193.9958   $194.00   $194.00   $194.00  
  Purchase #4 $224.91   10.641%   $248.8427   $248.84   $248.85   $248.80  
  Purchase #5 $14.46   10.274%   $15.9456   $15.95   $15.95   $15.90  
  Purchase #6 $168.30   9.131%   $183.6675   $183.67   $183.65   $183.70  
  Purchase #7 $116.56   6.622%   $124.2786   $124.28   $124.30   $124.30  
  7 purchase totals = $1,024.93       $1,112.3605   $1,112.37   $1,112.35   $1,112.40