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 $52.67   11.134%   $58.5343   $58.53   $58.55   $58.50  
  Purchase #2 $235.73   12.527%   $265.2599   $265.26   $265.25   $265.30  
  Purchase #3 $239.49   5.460%   $252.5662   $252.57   $252.55   $252.60  
  Purchase #4 $234.89   3.377%   $242.8222   $242.82   $242.80   $242.80  
  Purchase #5 $18.57   10.641%   $20.546   $20.55   $20.55   $20.50  
  Purchase #6 $93.93   12.723%   $105.8807   $105.88   $105.90   $105.90  
  Purchase #7 $150.25   12.354%   $168.8119   $168.81   $168.80   $168.80  
  7 purchase totals = $1,025.53       $1,114.4212   $1,114.42   $1,114.40   $1,114.40