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 $85.78   12.628%   $96.6123   $96.61   $96.60   $96.60  
  Purchase #2 $239.62   5.551%   $252.9213   $252.92   $252.90   $252.90  
  Purchase #3 $211.93   6.531%   $225.7711   $225.77   $225.75   $225.80  
  Purchase #4 $50.86   3.520%   $52.6503   $52.65   $52.65   $52.70  
  Purchase #5 $206.29   5.821%   $218.2981   $218.30   $218.30   $218.30  
  Purchase #6 $247.44   3.576%   $256.2885   $256.29   $256.30   $256.30  
  Purchase #7 $103.87   4.695%   $108.7467   $108.75   $108.75   $108.70  
  7 purchase totals = $1,145.79       $1,211.2883   $1,211.29   $1,211.25   $1,211.30