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	$63.25	12.526%	$71.1727	$71.17	$71.15	$71.20
Purchase #2	$107.70	13.782%	$122.5432	$122.54	$122.55	$122.50
Purchase #3	$176.41	4.573%	$184.4772	$184.48	$184.50	$184.50
Purchase #4	$202.50	6.275%	$215.2069	$215.21	$215.20	$215.20
Purchase #5	$73.46	6.731%	$78.4046	$78.40	$78.40	$78.40
Purchase #6	$51.36	4.483%	$53.6625	$53.66	$53.65	$53.70
Purchase #7	$174.68	12.204%	$195.9979	$196.00	$196.00	$196.00
7 purchase totals =	$849.36		$921.4650	$921.46	$921.45	$921.50