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	$99.59	11.732%	$111.2739	$111.27	$111.25	$111.30
Purchase #2	$46.99	12.213%	$52.7289	$52.73	$52.75	$52.70
Purchase #3	$37.35	12.420%	$41.9889	$41.99	$42.00	$42.00
Purchase #4	$80.49	12.435%	$90.4989	$90.50	$90.50	$90.50
Purchase #5	$178.37	4.301%	$186.0417	$186.04	$186.05	$186.00
Purchase #6	$221.54	11.154%	$246.2506	$246.25	$246.25	$246.30
Purchase #7	$145.26	8.277%	$157.2832	$157.28	$157.30	$157.30
7 purchase totals =	$809.59		$886.0661	$886.06	$886.10	$886.10