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	$86.87	4.593%	$90.8599	$90.86	$90.85	$90.90
Purchase #2	$175.73	5.502%	$185.3987	$185.40	$185.40	$185.40
Purchase #3	$141.72	10.190%	$156.1613	$156.16	$156.15	$156.20
Purchase #4	$168.62	13.364%	$191.1544	$191.15	$191.15	$191.20
Purchase #5	$11.46	12.593%	$12.9032	$12.90	$12.90	$12.90
Purchase #6	$199.67	9.134%	$217.9079	$217.91	$217.90	$217.90
Purchase #7	$233.29	13.324%	$264.3736	$264.37	$264.35	$264.40
7 purchase totals =	$1,017.36		$1,118.7590	$1,118.75	$1,118.70	$1,118.90