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 $104.60   10.834%   $115.9324   $115.93   $115.95   $115.90  
  Purchase #2 $148.45   13.147%   $167.9667   $167.97   $167.95   $168.00  
  Purchase #3 $153.36   5.857%   $162.3423   $162.34   $162.35   $162.30  
  Purchase #4 $155.25   7.710%   $167.2198   $167.22   $167.20   $167.20  
  Purchase #5 $60.37   8.613%   $65.5697   $65.57   $65.55   $65.60  
  Purchase #6 $126.59   7.115%   $135.5969   $135.60   $135.60   $135.60  
  Purchase #7 $182.42   12.460%   $205.1495   $205.15   $205.15   $205.10  
  7 purchase totals = $931.04       $1,019.7773   $1,019.78   $1,019.75   $1,019.70