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 $76.81   8.591%   $83.4087   $83.41   $83.40   $83.40  
  Purchase #2 $211.74   5.427%   $223.2311   $223.23   $223.25   $223.20  
  Purchase #3 $138.60   9.419%   $151.6547   $151.65   $151.65   $151.70  
  Purchase #4 $118.82   6.336%   $126.3484   $126.35   $126.35   $126.30  
  Purchase #5 $62.87   11.187%   $69.9033   $69.90   $69.90   $69.90  
  Purchase #6 $207.73   9.155%   $226.7477   $226.75   $226.75   $226.70  
  Purchase #7 $11.55   10.177%   $12.7254   $12.73   $12.75   $12.70  
  7 purchase totals = $828.12       $894.0193   $894.02   $894.05   $893.90