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	$81.89	5.477%	$86.3751	$86.38	$86.40	$86.40
Purchase #2	$131.43	10.826%	$145.6586	$145.66	$145.65	$145.70
Purchase #3	$88.35	10.688%	$97.7928	$97.79	$97.80	$97.80
Purchase #4	$67.36	6.484%	$71.7276	$71.73	$71.75	$71.70
Purchase #5	$234.80	9.674%	$257.5146	$257.51	$257.50	$257.50
Purchase #6	$35.61	4.599%	$37.2477	$37.25	$37.25	$37.20
Purchase #7	$214.29	4.137%	$223.1552	$223.16	$223.15	$223.20
7 purchase totals =	$853.73		$919.4716	$919.48	$919.50	$919.50