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 $219.80   3.222%   $226.882   $226.88   $226.90   $226.90  
  Purchase #2 $49.52   12.242%   $55.5822   $55.58   $55.60   $55.60  
  Purchase #3 $86.40   11.567%   $96.3939   $96.39   $96.40   $96.40  
  Purchase #4 $207.30   7.507%   $222.862   $222.86   $222.85   $222.90  
  Purchase #5 $37.36   10.695%   $41.3557   $41.36   $41.35   $41.40  
  Purchase #6 $189.43   13.259%   $214.5465   $214.55   $214.55   $214.50  
  Purchase #7 $176.50   12.232%   $198.0895   $198.09   $198.10   $198.10  
  7 purchase totals = $966.31       $1,055.7118   $1,055.71   $1,055.75   $1,055.80