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	$170.84	6.650%	$182.2009	$182.20	$182.20	$182.20
Purchase #2	$238.69	6.208%	$253.5079	$253.51	$253.50	$253.50
Purchase #3	$76.82	5.791%	$81.2686	$81.27	$81.25	$81.30
Purchase #4	$198.55	10.535%	$219.4672	$219.47	$219.45	$219.50
Purchase #5	$197.40	12.546%	$222.1658	$222.17	$222.15	$222.20
Purchase #6	$145.88	11.396%	$162.5045	$162.50	$162.50	$162.50
Purchase #7	$134.72	13.501%	$152.9085	$152.91	$152.90	$152.90
7 purchase totals =	$1,162.90		$1,274.0234	$1,274.03	$1,273.95	$1,274.10