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	$90.30	7.727%	$97.2775	$97.28	$97.30	$97.30
Purchase #2	$37.46	3.148%	$38.6392	$38.64	$38.65	$38.60
Purchase #3	$80.63	9.812%	$88.5414	$88.54	$88.55	$88.50
Purchase #4	$155.38	11.445%	$173.1632	$173.16	$173.15	$173.20
Purchase #5	$82.52	7.757%	$88.9211	$88.92	$88.90	$88.90
Purchase #6	$218.58	5.198%	$229.9418	$229.94	$229.95	$229.90
Purchase #7	$249.78	6.309%	$265.5386	$265.54	$265.55	$265.50
7 purchase totals =	$914.65		$982.0228	$982.02	$982.05	$981.90