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	$30.69	6.274%	$32.6155	$32.62	$32.60	$32.60
Purchase #2	$17.34	4.690%	$18.1532	$18.15	$18.15	$18.20
Purchase #3	$185.56	7.531%	$199.5345	$199.53	$199.55	$199.50
Purchase #4	$129.61	7.718%	$139.6133	$139.61	$139.60	$139.60
Purchase #5	$178.41	3.756%	$185.1111	$185.11	$185.10	$185.10
Purchase #6	$171.76	3.207%	$177.2683	$177.27	$177.25	$177.30
Purchase #7	$40.37	10.251%	$44.5083	$44.51	$44.50	$44.50
7 purchase totals =	$753.74		$796.8042	$796.80	$796.75	$796.80