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	$27.30	5.282%	$28.742	$28.74	$28.75	$28.70
Purchase #2	$106.43	5.322%	$112.0942	$112.09	$112.10	$112.10
Purchase #3	$249.66	7.867%	$269.3008	$269.30	$269.30	$269.30
Purchase #4	$30.59	7.147%	$32.7763	$32.78	$32.80	$32.80
Purchase #5	$9.85	7.167%	$10.5559	$10.56	$10.55	$10.60
Purchase #6	$128.96	10.240%	$142.1655	$142.17	$142.15	$142.20
Purchase #7	$48.98	9.818%	$53.7889	$53.79	$53.80	$53.80
7 purchase totals =	$601.77		$649.4236	$649.43	$649.45	$649.50