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 $226.90   13.379%   $257.257   $257.26   $257.25   $257.30  
  Purchase #2 $233.46   6.588%   $248.8403   $248.84   $248.85   $248.80  
  Purchase #3 $243.38   5.671%   $257.1821   $257.18   $257.20   $257.20  
  Purchase #4 $43.98   6.728%   $46.939   $46.94   $46.95   $46.90  
  Purchase #5 $152.63   8.708%   $165.921   $165.92   $165.90   $165.90  
  Purchase #6 $96.67   11.241%   $107.5367   $107.54   $107.55   $107.50  
  Purchase #7 $67.52   7.636%   $72.6758   $72.68   $72.70   $72.70  
  7 purchase totals = $1,064.54       $1,156.3519   $1,156.36   $1,156.40   $1,156.30