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	$141.50	10.167%	$155.8863	$155.89	$155.90	$155.90
Purchase #2	$86.43	6.568%	$92.1067	$92.11	$92.10	$92.10
Purchase #3	$34.38	11.388%	$38.2952	$38.30	$38.30	$38.30
Purchase #4	$19.79	8.517%	$21.4755	$21.48	$21.50	$21.50
Purchase #5	$144.59	11.306%	$160.9373	$160.94	$160.95	$160.90
Purchase #6	$60.39	11.492%	$67.33	$67.33	$67.35	$67.30
Purchase #7	$30.73	9.200%	$33.5572	$33.56	$33.55	$33.60
7 purchase totals =	$517.81		$569.5882	$569.61	$569.65	$569.60