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 $240.98   9.373%   $263.5671   $263.57   $263.55   $263.60  
  Purchase #2 $56.59   5.863%   $59.9079   $59.91   $59.90   $59.90  
  Purchase #3 $202.56   10.259%   $223.3406   $223.34   $223.35   $223.30  
  Purchase #4 $66.34   6.145%   $70.4166   $70.42   $70.40   $70.40  
  Purchase #5 $248.66   8.577%   $269.9876   $269.99   $270.00   $270.00  
  Purchase #6 $212.28   6.549%   $226.1822   $226.18   $226.20   $226.20  
  Purchase #7 $30.41   9.739%   $33.3716   $33.37   $33.35   $33.40  
  7 purchase totals = $1,057.82       $1,146.7736   $1,146.78   $1,146.75   $1,146.80