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 $219.65   11.856%   $245.6917   $245.69   $245.70   $245.70  
  Purchase #2 $6.39   4.561%   $6.6814   $6.68   $6.70   $6.70  
  Purchase #3 $47.89   12.636%   $53.9414   $53.94   $53.95   $53.90  
  Purchase #4 $41.77   13.746%   $47.5117   $47.51   $47.50   $47.50  
  Purchase #5 $187.58   12.116%   $210.3072   $210.31   $210.30   $210.30  
  Purchase #6 $246.94   5.511%   $260.5489   $260.55   $260.55   $260.50  
  Purchase #7 $113.72   5.158%   $119.5857   $119.59   $119.60   $119.60  
  7 purchase totals = $863.94       $944.2680   $944.27   $944.30   $944.20