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 $88.30   9.493%   $96.6823   $96.68   $96.70   $96.70  
  Purchase #2 $53.26   10.433%   $58.8166   $58.82   $58.80   $58.80  
  Purchase #3 $69.66   13.667%   $79.1804   $79.18   $79.20   $79.20  
  Purchase #4 $248.98   6.378%   $264.8599   $264.86   $264.85   $264.90  
  Purchase #5 $185.69   4.210%   $193.5075   $193.51   $193.50   $193.50  
  Purchase #6 $194.77   5.806%   $206.0783   $206.08   $206.10   $206.10  
  Purchase #7 $247.51   13.782%   $281.6218   $281.62   $281.60   $281.60  
  7 purchase totals = $1,088.17       $1,180.7468   $1,180.75   $1,180.75   $1,180.80