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 $63.35   7.262%   $67.9505   $67.95   $67.95   $68.00  
  Purchase #2 $76.65   5.202%   $80.6373   $80.64   $80.65   $80.60  
  Purchase #3 $210.33   8.808%   $228.8559   $228.86   $228.85   $228.90  
  Purchase #4 $30.67   11.406%   $34.1682   $34.17   $34.15   $34.20  
  Purchase #5 $213.50   3.249%   $220.4366   $220.44   $220.45   $220.40  
  Purchase #6 $167.99   6.389%   $178.7229   $178.72   $178.70   $178.70  
  Purchase #7 $14.40   6.182%   $15.2902   $15.29   $15.30   $15.30  
  7 purchase totals = $776.89       $826.0616   $826.07   $826.05   $826.10