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 $49.49   8.298%   $53.5967   $53.60   $53.60   $53.60  
  Purchase #2 $160.44   10.603%   $177.4515   $177.45   $177.45   $177.50  
  Purchase #3 $127.51   7.816%   $137.4762   $137.48   $137.50   $137.50  
  Purchase #4 $101.74   7.205%   $109.0704   $109.07   $109.05   $109.10  
  Purchase #5 $90.27   12.169%   $101.255   $101.26   $101.25   $101.30  
  Purchase #6 $210.67   5.756%   $222.7962   $222.80   $222.80   $222.80  
  Purchase #7 $162.88   12.535%   $183.297   $183.30   $183.30   $183.30  
  7 purchase totals = $903.00       $984.9430   $984.96   $984.95   $985.10