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 $236.51   10.832%   $262.1288   $262.13   $262.15   $262.10  
  Purchase #2 $170.60   5.453%   $179.9028   $179.90   $179.90   $179.90  
  Purchase #3 $104.96   8.242%   $113.6108   $113.61   $113.60   $113.60  
  Purchase #4 $145.93   10.608%   $161.4103   $161.41   $161.40   $161.40  
  Purchase #5 $5.95   13.586%   $6.7584   $6.76   $6.75   $6.80  
  Purchase #6 $182.67   7.540%   $196.4433   $196.44   $196.45   $196.40  
  Purchase #7 $223.53   4.252%   $233.0345   $233.03   $233.05   $233.00  
  7 purchase totals = $1,070.15       $1,153.2889   $1,153.28   $1,153.30   $1,153.20