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	$135.37	13.340%	$153.4284	$153.43	$153.45	$153.40
Purchase #2	$95.98	10.756%	$106.3036	$106.30	$106.30	$106.30
Purchase #3	$33.94	5.377%	$35.765	$35.77	$35.75	$35.80
Purchase #4	$171.71	7.530%	$184.6398	$184.64	$184.65	$184.60
Purchase #5	$245.38	5.179%	$258.0882	$258.09	$258.10	$258.10
Purchase #6	$53.46	10.690%	$59.1749	$59.17	$59.15	$59.20
Purchase #7	$36.44	11.426%	$40.6036	$40.60	$40.60	$40.60
7 purchase totals =	$772.28		$838.0035	$838.00	$838.00	$838.00