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	$10.35	3.757%	$10.7388	$10.74	$10.75	$10.70
Purchase #2	$42.72	7.324%	$45.8488	$45.85	$45.85	$45.80
Purchase #3	$224.32	13.110%	$253.7284	$253.73	$253.75	$253.70
Purchase #4	$203.79	9.495%	$223.1399	$223.14	$223.15	$223.10
Purchase #5	$61.63	9.549%	$67.515	$67.52	$67.50	$67.50
Purchase #6	$162.70	12.684%	$183.3369	$183.34	$183.35	$183.30
Purchase #7	$178.30	7.288%	$191.2945	$191.29	$191.30	$191.30
7 purchase totals =	$883.81		$975.6023	$975.61	$975.65	$975.40