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	$135.74	4.351%	$141.646	$141.65	$141.65	$141.60
Purchase #2	$183.89	6.459%	$195.7675	$195.77	$195.75	$195.80
Purchase #3	$74.57	4.379%	$77.8354	$77.84	$77.85	$77.80
Purchase #4	$40.40	12.654%	$45.5122	$45.51	$45.50	$45.50
Purchase #5	$16.58	9.436%	$18.1445	$18.14	$18.15	$18.10
Purchase #6	$70.64	4.325%	$73.6952	$73.70	$73.70	$73.70
Purchase #7	$86.56	3.455%	$89.5506	$89.55	$89.55	$89.60
7 purchase totals =	$608.38		$642.1514	$642.16	$642.15	$642.10