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	$88.31	9.280%	$96.5052	$96.51	$96.50	$96.50
Purchase #2	$240.44	6.650%	$256.4293	$256.43	$256.45	$256.40
Purchase #3	$147.59	8.164%	$159.6392	$159.64	$159.65	$159.60
Purchase #4	$105.99	4.668%	$110.9376	$110.94	$110.95	$110.90
Purchase #5	$153.78	11.312%	$171.1756	$171.18	$171.20	$171.20
Purchase #6	$229.33	10.418%	$253.2216	$253.22	$253.20	$253.20
Purchase #7	$31.67	5.749%	$33.4907	$33.49	$33.50	$33.50
7 purchase totals =	$997.11		$1,081.3992	$1,081.41	$1,081.45	$1,081.30