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 $62.39   10.531%   $68.9603   $68.96   $68.95   $69.00  
  Purchase #2 $147.91   10.803%   $163.8887   $163.89   $163.90   $163.90  
  Purchase #3 $217.44   3.169%   $224.3307   $224.33   $224.35   $224.30  
  Purchase #4 $115.32   4.137%   $120.0908   $120.09   $120.10   $120.10  
  Purchase #5 $65.54   3.226%   $67.6543   $67.65   $67.65   $67.70  
  Purchase #6 $177.59   6.423%   $188.9966   $189.00   $189.00   $189.00  
  Purchase #7 $27.82   4.745%   $29.1401   $29.14   $29.15   $29.10  
  7 purchase totals = $814.01       $863.0615   $863.06   $863.10   $863.10