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 $9.25   7.636%   $9.9563   $9.96   $9.95   $10.00  
  Purchase #2 $101.56   12.561%   $114.317   $114.32   $114.30   $114.30  
  Purchase #3 $58.74   8.548%   $63.7611   $63.76   $63.75   $63.80  
  Purchase #4 $18.27   7.487%   $19.6379   $19.64   $19.65   $19.60  
  Purchase #5 $25.47   7.144%   $27.2896   $27.29   $27.30   $27.30  
  Purchase #6 $230.93   6.203%   $245.2546   $245.25   $245.25   $245.30  
  Purchase #7 $156.58   6.733%   $167.1225   $167.12   $167.10   $167.10  
  7 purchase totals = $600.80       $647.3390   $647.34   $647.30   $647.40