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	$66.74	6.453%	$71.0467	$71.05	$71.05	$71.00
Purchase #2	$220.96	3.539%	$228.7798	$228.78	$228.80	$228.80
Purchase #3	$164.70	5.215%	$173.2891	$173.29	$173.30	$173.30
Purchase #4	$105.84	13.665%	$120.303	$120.30	$120.30	$120.30
Purchase #5	$211.64	5.312%	$222.8823	$222.88	$222.90	$222.90
Purchase #6	$184.63	6.335%	$196.3263	$196.33	$196.35	$196.30
Purchase #7	$76.99	4.307%	$80.306	$80.31	$80.30	$80.30
7 purchase totals =	$1,031.50		$1,092.9332	$1,092.94	$1,093.00	$1,092.90