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 $203.71   9.292%   $222.6387   $222.64   $222.65   $222.60  
  Purchase #2 $248.78   8.301%   $269.4312   $269.43   $269.45   $269.40  
  Purchase #3 $214.33   6.108%   $227.4213   $227.42   $227.40   $227.40  
  Purchase #4 $111.89   7.493%   $120.2739   $120.27   $120.25   $120.30  
  Purchase #5 $132.80   5.744%   $140.428   $140.43   $140.45   $140.40  
  Purchase #6 $207.59   8.133%   $224.4733   $224.47   $224.45   $224.50  
  Purchase #7 $63.75   7.158%   $68.3132   $68.31   $68.30   $68.30  
  7 purchase totals = $1,182.85       $1,272.9796   $1,272.97   $1,272.95   $1,272.90