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	$96.72	3.728%	$100.3257	$100.33	$100.35	$100.30
Purchase #2	$105.89	12.326%	$118.942	$118.94	$118.95	$118.90
Purchase #3	$58.81	5.138%	$61.8317	$61.83	$61.85	$61.80
Purchase #4	$109.44	3.500%	$113.2704	$113.27	$113.25	$113.30
Purchase #5	$41.30	4.843%	$43.3002	$43.30	$43.30	$43.30
Purchase #6	$91.81	4.678%	$96.1049	$96.10	$96.10	$96.10
Purchase #7	$84.87	10.414%	$93.7084	$93.71	$93.70	$93.70
7 purchase totals =	$588.84		$627.4833	$627.48	$627.50	$627.40