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 $169.54   8.224%   $183.483   $183.48   $183.50   $183.50  
  Purchase #2 $116.94   8.524%   $126.908   $126.91   $126.90   $126.90  
  Purchase #3 $233.99   7.180%   $250.7905   $250.79   $250.80   $250.80  
  Purchase #4 $243.34   9.326%   $266.0339   $266.03   $266.05   $266.00  
  Purchase #5 $195.59   11.494%   $218.0711   $218.07   $218.05   $218.10  
  Purchase #6 $163.50   13.123%   $184.9561   $184.96   $184.95   $185.00  
  Purchase #7 $131.80   5.385%   $138.8974   $138.90   $138.90   $138.90  
  7 purchase totals = $1,254.70       $1,369.1400   $1,369.14   $1,369.15   $1,369.20