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 $69.33   11.484%   $77.2919   $77.29   $77.30   $77.30  
  Purchase #2 $57.32   9.494%   $62.762   $62.76   $62.75   $62.80  
  Purchase #3 $248.25   8.471%   $269.2793   $269.28   $269.30   $269.30  
  Purchase #4 $98.90   5.477%   $104.3168   $104.32   $104.30   $104.30  
  Purchase #5 $63.45   9.846%   $69.6973   $69.70   $69.70   $69.70  
  Purchase #6 $194.25   10.510%   $214.6657   $214.67   $214.65   $214.70  
  Purchase #7 $149.46   8.862%   $162.7051   $162.71   $162.70   $162.70  
  7 purchase totals = $880.96       $960.7181   $960.73   $960.70   $960.80