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	$66.67	5.799%	$70.5362	$70.54	$70.55	$70.50
Purchase #2	$73.88	6.710%	$78.8373	$78.84	$78.85	$78.80
Purchase #3	$37.84	7.662%	$40.7393	$40.74	$40.75	$40.70
Purchase #4	$208.32	10.281%	$229.7374	$229.74	$229.75	$229.70
Purchase #5	$239.75	5.699%	$253.4134	$253.41	$253.40	$253.40
Purchase #6	$96.73	4.344%	$100.932	$100.93	$100.95	$100.90
Purchase #7	$76.74	6.772%	$81.9368	$81.94	$81.95	$81.90
7 purchase totals =	$799.93		$856.1324	$856.14	$856.20	$855.90