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 $61.66   13.271%   $69.8429   $69.84   $69.85   $69.80  
  Purchase #2 $143.38   13.296%   $162.4438   $162.44   $162.45   $162.40  
  Purchase #3 $210.40   12.206%   $236.0814   $236.08   $236.10   $236.10  
  Purchase #4 $129.88   6.471%   $138.2845   $138.28   $138.30   $138.30  
  Purchase #5 $33.93   10.563%   $37.514   $37.51   $37.50   $37.50  
  Purchase #6 $247.28   9.110%   $269.8072   $269.81   $269.80   $269.80  
  Purchase #7 $67.77   8.356%   $73.4329   $73.43   $73.45   $73.40  
  7 purchase totals = $894.30       $987.4067   $987.39   $987.45   $987.30