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 $176.26   5.339%   $185.6705   $185.67   $185.65   $185.70  
  Purchase #2 $54.69   7.553%   $58.8207   $58.82   $58.80   $58.80  
  Purchase #3 $67.55   5.844%   $71.4976   $71.50   $71.50   $71.50  
  Purchase #4 $26.45   5.558%   $27.9201   $27.92   $27.90   $27.90  
  Purchase #5 $207.36   9.245%   $226.5304   $226.53   $226.55   $226.50  
  Purchase #6 $152.62   8.209%   $165.1486   $165.15   $165.15   $165.10  
  Purchase #7 $164.86   3.712%   $170.9796   $170.98   $171.00   $171.00  
  7 purchase totals = $849.79       $906.5675   $906.57   $906.55   $906.50