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 $86.96   11.231%   $96.7265   $96.73   $96.75   $96.70  
  Purchase #2 $174.48   10.711%   $193.1686   $193.17   $193.15   $193.20  
  Purchase #3 $11.48   13.385%   $13.0166   $13.02   $13.00   $13.00  
  Purchase #4 $69.89   13.627%   $79.4139   $79.41   $79.40   $79.40  
  Purchase #5 $37.47   3.539%   $38.7961   $38.80   $38.80   $38.80  
  Purchase #6 $97.88   7.325%   $105.0497   $105.05   $105.05   $105.00  
  Purchase #7 $246.37   11.687%   $275.1633   $275.16   $275.15   $275.20  
  7 purchase totals = $724.53       $801.3347   $801.34   $801.30   $801.30