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	$19.90	5.345%	$20.9637	$20.96	$20.95	$21.00
Purchase #2	$111.70	11.511%	$124.5578	$124.56	$124.55	$124.60
Purchase #3	$97.25	4.274%	$101.4065	$101.41	$101.40	$101.40
Purchase #4	$21.39	7.359%	$22.9641	$22.96	$22.95	$23.00
Purchase #5	$54.76	3.277%	$56.5545	$56.55	$56.55	$56.60
Purchase #6	$64.60	5.138%	$67.9191	$67.92	$67.90	$67.90
Purchase #7	$77.56	3.845%	$80.5422	$80.54	$80.55	$80.50
7 purchase totals =	$447.16		$474.9079	$474.90	$474.85	$475.00