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 $116.34   10.337%   $128.3661   $128.37   $128.35   $128.40  
  Purchase #2 $91.61   7.803%   $98.7583   $98.76   $98.75   $98.80  
  Purchase #3 $77.48   5.534%   $81.7677   $81.77   $81.75   $81.80  
  Purchase #4 $6.40   12.460%   $7.1974   $7.20   $7.20   $7.20  
  Purchase #5 $163.36   5.738%   $172.7336   $172.73   $172.75   $172.70  
  Purchase #6 $163.32   4.379%   $170.4718   $170.47   $170.45   $170.50  
  Purchase #7 $24.44   10.704%   $27.0561   $27.06   $27.05   $27.10  
  7 purchase totals = $642.95       $686.3510   $686.36   $686.30   $686.50