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 $37.61   5.425%   $39.6503   $39.65   $39.65   $39.70  
  Purchase #2 $198.47   3.622%   $205.6586   $205.66   $205.65   $205.70  
  Purchase #3 $61.51   8.489%   $66.7316   $66.73   $66.75   $66.70  
  Purchase #4 $204.81   11.475%   $228.3119   $228.31   $228.30   $228.30  
  Purchase #5 $175.47   5.471%   $185.07   $185.07   $185.05   $185.10  
  Purchase #6 $58.47   13.717%   $66.4903   $66.49   $66.50   $66.50  
  Purchase #7 $8.72   11.526%   $9.7251   $9.73   $9.75   $9.70  
  7 purchase totals = $745.06       $801.6378   $801.64   $801.65   $801.70