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	$18.62	11.376%	$20.7382	$20.74	$20.75	$20.70
Purchase #2	$30.32	3.125%	$31.2675	$31.27	$31.25	$31.30
Purchase #3	$98.64	9.766%	$108.2732	$108.27	$108.25	$108.30
Purchase #4	$64.64	4.313%	$67.4279	$67.43	$67.45	$67.40
Purchase #5	$192.33	8.176%	$208.0549	$208.05	$208.05	$208.10
Purchase #6	$24.75	10.760%	$27.4131	$27.41	$27.40	$27.40
Purchase #7	$85.30	7.138%	$91.3887	$91.39	$91.40	$91.40
7 purchase totals =	$514.60		$554.5635	$554.56	$554.55	$554.60