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 $18.32   6.617%   $19.5322   $19.53   $19.55   $19.50  
  Purchase #2 $106.57   7.632%   $114.7034   $114.70   $114.70   $114.70  
  Purchase #3 $103.36   8.779%   $112.434   $112.43   $112.45   $112.40  
  Purchase #4 $166.99   13.659%   $189.7992   $189.80   $189.80   $189.80  
  Purchase #5 $148.34   5.691%   $156.782   $156.78   $156.80   $156.80  
  Purchase #6 $221.29   11.207%   $246.09   $246.09   $246.10   $246.10  
  Purchase #7 $93.64   12.388%   $105.2401   $105.24   $105.25   $105.20  
  7 purchase totals = $858.51       $944.5809   $944.57   $944.65   $944.50