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 $105.34   13.332%   $119.3839   $119.38   $119.40   $119.40  
  Purchase #2 $245.61   11.353%   $273.4941   $273.49   $273.50   $273.50  
  Purchase #3 $55.44   6.352%   $58.9615   $58.96   $58.95   $59.00  
  Purchase #4 $181.42   6.828%   $193.8074   $193.81   $193.80   $193.80  
  Purchase #5 $165.28   3.171%   $170.521   $170.52   $170.50   $170.50  
  Purchase #6 $114.82   5.484%   $121.1167   $121.12   $121.10   $121.10  
  Purchase #7 $85.63   6.352%   $91.0692   $91.07   $91.05   $91.10  
  7 purchase totals = $953.54       $1,028.3538   $1,028.35   $1,028.30   $1,028.40