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 $201.53   3.242%   $208.0636   $208.06   $208.05   $208.10  
  Purchase #2 $41.94   8.606%   $45.5494   $45.55   $45.55   $45.50  
  Purchase #3 $16.78   9.542%   $18.3811   $18.38   $18.40   $18.40  
  Purchase #4 $138.48   7.813%   $149.2994   $149.30   $149.30   $149.30  
  Purchase #5 $72.80   12.805%   $82.122   $82.12   $82.10   $82.10  
  Purchase #6 $135.64   4.843%   $142.209   $142.21   $142.20   $142.20  
  Purchase #7 $7.96   5.309%   $8.3826   $8.38   $8.40   $8.40  
  7 purchase totals = $615.13       $654.0071   $654.00   $654.00   $654.00