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 $72.67   10.295%   $80.1514   $80.15   $80.15   $80.20  
  Purchase #2 $248.39   4.444%   $259.4285   $259.43   $259.45   $259.40  
  Purchase #3 $58.65   13.806%   $66.7472   $66.75   $66.75   $66.70  
  Purchase #4 $226.79   5.773%   $239.8826   $239.88   $239.90   $239.90  
  Purchase #5 $88.58   9.275%   $96.7958   $96.80   $96.80   $96.80  
  Purchase #6 $202.92   11.227%   $225.7018   $225.70   $225.70   $225.70  
  Purchase #7 $115.62   9.611%   $126.7322   $126.73   $126.75   $126.70  
  7 purchase totals = $1,013.62       $1,095.4395   $1,095.44   $1,095.50   $1,095.40