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	$30.41	8.211%	$32.907	$32.91	$32.90	$32.90
Purchase #2	$145.93	11.618%	$162.8841	$162.88	$162.90	$162.90
Purchase #3	$246.57	11.764%	$275.5765	$275.58	$275.60	$275.60
Purchase #4	$40.44	8.351%	$43.8171	$43.82	$43.80	$43.80
Purchase #5	$234.54	3.533%	$242.8263	$242.83	$242.85	$242.80
Purchase #6	$159.49	12.257%	$179.0387	$179.04	$179.05	$179.00
Purchase #7	$199.38	7.495%	$214.3235	$214.32	$214.30	$214.30
7 purchase totals =	$1,056.76		$1,151.3732	$1,151.38	$1,151.40	$1,151.30