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	$218.71	10.836%	$242.4094	$242.41	$242.40	$242.40
Purchase #2	$250.49	6.107%	$265.7874	$265.79	$265.80	$265.80
Purchase #3	$19.36	7.513%	$20.8145	$20.81	$20.80	$20.80
Purchase #4	$124.57	8.284%	$134.8894	$134.89	$134.90	$134.90
Purchase #5	$101.41	8.383%	$109.9112	$109.91	$109.90	$109.90
Purchase #6	$199.36	11.818%	$222.9204	$222.92	$222.90	$222.90
Purchase #7	$152.72	11.698%	$170.5852	$170.59	$170.60	$170.60
7 purchase totals =	$1,066.62		$1,167.3175	$1,167.32	$1,167.30	$1,167.30