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	$46.41	8.857%	$50.5205	$50.52	$50.50	$50.50
Purchase #2	$98.35	12.492%	$110.6359	$110.64	$110.65	$110.60
Purchase #3	$219.86	3.686%	$227.964	$227.96	$227.95	$228.00
Purchase #4	$13.72	11.472%	$15.294	$15.29	$15.30	$15.30
Purchase #5	$40.57	3.601%	$42.0309	$42.03	$42.05	$42.00
Purchase #6	$55.91	10.121%	$61.5687	$61.57	$61.55	$61.60
Purchase #7	$79.78	8.241%	$86.3547	$86.35	$86.35	$86.40
7 purchase totals =	$554.60		$594.3687	$594.36	$594.35	$594.40