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 $94.71   11.512%   $105.613   $105.61   $105.60   $105.60  
  Purchase #2 $225.28   8.673%   $244.8185   $244.82   $244.80   $244.80  
  Purchase #3 $53.57   5.176%   $56.3428   $56.34   $56.35   $56.30  
  Purchase #4 $20.45   7.778%   $22.0406   $22.04   $22.05   $22.00  
  Purchase #5 $182.56   4.789%   $191.3028   $191.30   $191.30   $191.30  
  Purchase #6 $230.89   3.539%   $239.0612   $239.06   $239.05   $239.10  
  Purchase #7 $118.53   4.266%   $123.5865   $123.59   $123.60   $123.60  
  7 purchase totals = $925.99       $982.7654   $982.76   $982.75   $982.70