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	$170.57	11.666%	$190.4687	$190.47	$190.45	$190.50
Purchase #2	$90.87	9.688%	$99.6735	$99.67	$99.65	$99.70
Purchase #3	$22.25	13.666%	$25.2907	$25.29	$25.30	$25.30
Purchase #4	$76.42	9.259%	$83.4957	$83.50	$83.50	$83.50
Purchase #5	$63.68	13.703%	$72.4061	$72.41	$72.40	$72.40
Purchase #6	$230.73	7.654%	$248.3901	$248.39	$248.40	$248.40
Purchase #7	$65.26	6.183%	$69.295	$69.30	$69.30	$69.30
7 purchase totals =	$719.78		$789.0198	$789.03	$789.00	$789.10