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 $103.63   11.543%   $115.592   $115.59   $115.60   $115.60  
  Purchase #2 $130.36   4.120%   $135.7308   $135.73   $135.75   $135.70  
  Purchase #3 $168.98   9.439%   $184.93   $184.93   $184.95   $184.90  
  Purchase #4 $208.93   13.796%   $237.754   $237.75   $237.75   $237.80  
  Purchase #5 $228.74   4.288%   $238.5484   $238.55   $238.55   $238.50  
  Purchase #6 $131.90   11.671%   $147.294   $147.29   $147.30   $147.30  
  Purchase #7 $45.53   10.749%   $50.424   $50.42   $50.40   $50.40  
  7 purchase totals = $1,018.07       $1,110.2732   $1,110.26   $1,110.30   $1,110.20