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 $219.78   12.620%   $247.5162   $247.52   $247.50   $247.50  
  Purchase #2 $106.51   4.512%   $111.3157   $111.32   $111.30   $111.30  
  Purchase #3 $241.27   4.658%   $252.5084   $252.51   $252.50   $252.50  
  Purchase #4 $53.76   11.784%   $60.0951   $60.10   $60.10   $60.10  
  Purchase #5 $81.34   13.388%   $92.2298   $92.23   $92.25   $92.20  
  Purchase #6 $192.76   4.758%   $201.9315   $201.93   $201.95   $201.90  
  Purchase #7 $249.41   13.768%   $283.7488   $283.75   $283.75   $283.70  
  7 purchase totals = $1,144.83       $1,249.3455   $1,249.36   $1,249.35   $1,249.20