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 $232.42   4.687%   $243.3135   $243.31   $243.30   $243.30  
  Purchase #2 $30.37   5.476%   $32.0331   $32.03   $32.05   $32.00  
  Purchase #3 $198.43   6.633%   $211.5919   $211.59   $211.60   $211.60  
  Purchase #4 $114.99   7.629%   $123.7626   $123.76   $123.75   $123.80  
  Purchase #5 $202.60   6.727%   $216.2289   $216.23   $216.25   $216.20  
  Purchase #6 $162.30   12.369%   $182.3749   $182.37   $182.35   $182.40  
  Purchase #7 $13.96   7.261%   $14.9736   $14.97   $14.95   $15.00  
  7 purchase totals = $955.07       $1,024.2785   $1,024.26   $1,024.25   $1,024.30