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 $63.25   8.260%   $68.4745   $68.47   $68.45   $68.50  
  Purchase #2 $229.88   13.372%   $260.6196   $260.62   $260.60   $260.60  
  Purchase #3 $230.50   4.599%   $241.1007   $241.10   $241.10   $241.10  
  Purchase #4 $232.44   6.475%   $247.4905   $247.49   $247.50   $247.50  
  Purchase #5 $115.38   4.688%   $120.789   $120.79   $120.80   $120.80  
  Purchase #6 $65.38   10.523%   $72.2599   $72.26   $72.25   $72.30  
  Purchase #7 $18.48   11.132%   $20.5372   $20.54   $20.55   $20.50  
  7 purchase totals = $955.31       $1,031.2714   $1,031.27   $1,031.25   $1,031.30