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 $223.68   8.724%   $243.1938   $243.19   $243.20   $243.20  
  Purchase #2 $128.27   5.127%   $134.8464   $134.85   $134.85   $134.80  
  Purchase #3 $47.30   4.676%   $49.5117   $49.51   $49.50   $49.50  
  Purchase #4 $14.33   9.479%   $15.6883   $15.69   $15.70   $15.70  
  Purchase #5 $225.67   12.668%   $254.2579   $254.26   $254.25   $254.30  
  Purchase #6 $114.88   8.230%   $124.3346   $124.33   $124.35   $124.30  
  Purchase #7 $209.54   7.214%   $224.6562   $224.66   $224.65   $224.70  
  7 purchase totals = $963.67       $1,046.4889   $1,046.49   $1,046.50   $1,046.50