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	$74.82	3.451%	$77.402	$77.40	$77.40	$77.40
Purchase #2	$219.35	10.583%	$242.5638	$242.56	$242.55	$242.60
Purchase #3	$196.52	3.846%	$204.0782	$204.08	$204.10	$204.10
Purchase #4	$174.51	12.789%	$196.8281	$196.83	$196.85	$196.80
Purchase #5	$195.50	7.628%	$210.4127	$210.41	$210.40	$210.40
Purchase #6	$81.82	10.692%	$90.5682	$90.57	$90.55	$90.60
Purchase #7	$67.50	5.572%	$71.2611	$71.26	$71.25	$71.30
7 purchase totals =	$1,010.02		$1,093.1141	$1,093.11	$1,093.10	$1,093.20