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	$54.38	13.824%	$61.8975	$61.90	$61.90	$61.90
Purchase #2	$152.60	7.685%	$164.3273	$164.33	$164.35	$164.30
Purchase #3	$99.75	11.263%	$110.9848	$110.98	$111.00	$111.00
Purchase #4	$100.67	13.828%	$114.5906	$114.59	$114.60	$114.60
Purchase #5	$97.41	12.790%	$109.8687	$109.87	$109.85	$109.90
Purchase #6	$101.69	5.742%	$107.529	$107.53	$107.55	$107.50
Purchase #7	$109.42	11.766%	$122.2944	$122.29	$122.30	$122.30
7 purchase totals =	$715.92		$791.4923	$791.49	$791.55	$791.50