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	$127.36	4.826%	$133.5064	$133.51	$133.50	$133.50
Purchase #2	$65.51	10.282%	$72.2457	$72.25	$72.25	$72.20
Purchase #3	$237.56	4.199%	$247.5351	$247.54	$247.55	$247.50
Purchase #4	$177.55	4.522%	$185.5788	$185.58	$185.60	$185.60
Purchase #5	$52.50	10.682%	$58.1081	$58.11	$58.10	$58.10
Purchase #6	$147.88	11.486%	$164.8655	$164.87	$164.85	$164.90
Purchase #7	$47.41	11.535%	$52.8787	$52.88	$52.90	$52.90
7 purchase totals =	$855.77		$914.7183	$914.74	$914.75	$914.70