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	$76.74	4.833%	$80.4488	$80.45	$80.45	$80.40
Purchase #2	$59.45	9.537%	$65.1197	$65.12	$65.10	$65.10
Purchase #3	$38.77	6.720%	$41.3753	$41.38	$41.40	$41.40
Purchase #4	$212.25	5.516%	$223.9577	$223.96	$223.95	$224.00
Purchase #5	$224.32	7.502%	$241.1485	$241.15	$241.15	$241.10
Purchase #6	$202.92	13.152%	$229.608	$229.61	$229.60	$229.60
Purchase #7	$41.28	3.119%	$42.5675	$42.57	$42.55	$42.60
7 purchase totals =	$855.73		$924.2255	$924.24	$924.20	$924.20