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 $68.62   7.821%   $73.9868   $73.99   $74.00   $74.00  
  Purchase #2 $69.37   12.760%   $78.2216   $78.22   $78.20   $78.20  
  Purchase #3 $177.59   12.586%   $199.9415   $199.94   $199.95   $199.90  
  Purchase #4 $124.81   7.544%   $134.2257   $134.23   $134.25   $134.20  
  Purchase #5 $55.73   7.694%   $60.0179   $60.02   $60.00   $60.00  
  Purchase #6 $92.77   5.441%   $97.8176   $97.82   $97.80   $97.80  
  Purchase #7 $243.49   3.810%   $252.767   $252.77   $252.75   $252.80  
  7 purchase totals = $832.38       $896.9781   $896.99   $896.95   $896.90