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 $59.69   6.607%   $63.6337   $63.63   $63.65   $63.60  
  Purchase #2 $109.42   6.475%   $116.5049   $116.50   $116.50   $116.50  
  Purchase #3 $205.77   7.710%   $221.6349   $221.63   $221.65   $221.60  
  Purchase #4 $154.86   4.568%   $161.934   $161.93   $161.95   $161.90  
  Purchase #5 $181.39   11.718%   $202.6453   $202.65   $202.65   $202.60  
  Purchase #6 $159.80   9.556%   $175.0705   $175.07   $175.05   $175.10  
  Purchase #7 $229.45   8.473%   $248.8913   $248.89   $248.90   $248.90  
  7 purchase totals = $1,100.38       $1,190.3146   $1,190.30   $1,190.35   $1,190.20