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 $93.63   5.660%   $98.9295   $98.93   $98.95   $98.90  
  Purchase #2 $102.36   11.794%   $114.4323   $114.43   $114.45   $114.40  
  Purchase #3 $216.66   7.351%   $232.5867   $232.59   $232.60   $232.60  
  Purchase #4 $173.43   11.432%   $193.2565   $193.26   $193.25   $193.30  
  Purchase #5 $220.40   10.866%   $244.3487   $244.35   $244.35   $244.30  
  Purchase #6 $27.78   13.511%   $31.5334   $31.53   $31.55   $31.50  
  Purchase #7 $190.66   6.133%   $202.3532   $202.35   $202.35   $202.40  
  7 purchase totals = $1,024.92       $1,117.4403   $1,117.44   $1,117.50   $1,117.40