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	$70.51	12.493%	$79.3188	$79.32	$79.30	$79.30
Purchase #2	$56.45	13.547%	$64.0973	$64.10	$64.10	$64.10
Purchase #3	$229.73	10.606%	$254.0952	$254.10	$254.10	$254.10
Purchase #4	$92.99	7.702%	$100.1521	$100.15	$100.15	$100.20
Purchase #5	$136.32	3.839%	$141.5533	$141.55	$141.55	$141.60
Purchase #6	$42.70	6.666%	$45.5464	$45.55	$45.55	$45.50
Purchase #7	$71.33	13.274%	$80.7983	$80.80	$80.80	$80.80
7 purchase totals =	$700.03		$765.5614	$765.57	$765.55	$765.60