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	$93.86	4.215%	$97.8162	$97.82	$97.80	$97.80
Purchase #2	$240.31	12.790%	$271.0456	$271.05	$271.05	$271.00
Purchase #3	$173.52	7.251%	$186.1019	$186.10	$186.10	$186.10
Purchase #4	$209.49	11.820%	$234.2517	$234.25	$234.25	$234.30
Purchase #5	$153.55	5.703%	$162.307	$162.31	$162.30	$162.30
Purchase #6	$174.44	4.166%	$181.7072	$181.71	$181.70	$181.70
Purchase #7	$111.58	10.502%	$123.2981	$123.30	$123.30	$123.30
7 purchase totals =	$1,156.75		$1,256.5277	$1,256.54	$1,256.50	$1,256.50