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 $54.89   10.354%   $60.5733   $60.57   $60.55   $60.60  
  Purchase #2 $110.75   11.771%   $123.7864   $123.79   $123.80   $123.80  
  Purchase #3 $70.93   12.611%   $79.875   $79.88   $79.90   $79.90  
  Purchase #4 $48.42   4.672%   $50.6822   $50.68   $50.70   $50.70  
  Purchase #5 $211.63   13.176%   $239.5144   $239.51   $239.50   $239.50  
  Purchase #6 $205.70   9.349%   $224.9309   $224.93   $224.95   $224.90  
  Purchase #7 $200.99   13.873%   $228.8733   $228.87   $228.85   $228.90  
  7 purchase totals = $903.31       $1,008.2355   $1,008.23   $1,008.25   $1,008.30