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	$39.49	8.200%	$42.7282	$42.73	$42.75	$42.70
Purchase #2	$201.96	10.405%	$222.9739	$222.97	$222.95	$223.00
Purchase #3	$141.71	9.216%	$154.77	$154.77	$154.75	$154.80
Purchase #4	$57.31	9.522%	$62.7671	$62.77	$62.75	$62.80
Purchase #5	$79.75	11.777%	$89.1422	$89.14	$89.15	$89.10
Purchase #6	$95.40	5.544%	$100.689	$100.69	$100.70	$100.70
Purchase #7	$17.32	6.812%	$18.4998	$18.50	$18.50	$18.50
7 purchase totals =	$632.94		$691.5702	$691.57	$691.55	$691.60