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 $57.26   11.235%   $63.6932   $63.69   $63.70   $63.70  
  Purchase #2 $219.66   10.119%   $241.8874   $241.89   $241.90   $241.90  
  Purchase #3 $25.61   13.771%   $29.1368   $29.14   $29.15   $29.10  
  Purchase #4 $223.82   4.667%   $234.2657   $234.27   $234.25   $234.30  
  Purchase #5 $34.97   7.481%   $37.5861   $37.59   $37.60   $37.60  
  Purchase #6 $125.99   9.158%   $137.5282   $137.53   $137.55   $137.50  
  Purchase #7 $73.62   9.821%   $80.8502   $80.85   $80.85   $80.90  
  7 purchase totals = $760.93       $824.9476   $824.96   $825.00   $825.00