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 $204.59   10.469%   $226.0085   $226.01   $226.00   $226.00  
  Purchase #2 $193.84   12.810%   $218.6709   $218.67   $218.65   $218.70  
  Purchase #3 $77.42   10.590%   $85.6188   $85.62   $85.60   $85.60  
  Purchase #4 $139.33   6.332%   $148.1524   $148.15   $148.15   $148.20  
  Purchase #5 $168.82   11.847%   $188.8201   $188.82   $188.80   $188.80  
  Purchase #6 $248.93   8.564%   $270.2484   $270.25   $270.25   $270.20  
  Purchase #7 $142.54   4.370%   $148.769   $148.77   $148.75   $148.80  
  7 purchase totals = $1,175.47       $1,286.2881   $1,286.29   $1,286.20   $1,286.30