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	$29.63	5.533%	$31.2694	$31.27	$31.25	$31.30
Purchase #2	$54.72	8.487%	$59.3641	$59.36	$59.35	$59.40
Purchase #3	$248.49	10.732%	$275.1579	$275.16	$275.15	$275.20
Purchase #4	$38.40	4.382%	$40.0827	$40.08	$40.10	$40.10
Purchase #5	$78.84	12.315%	$88.5491	$88.55	$88.55	$88.50
Purchase #6	$219.28	13.511%	$248.9069	$248.91	$248.90	$248.90
Purchase #7	$179.69	10.772%	$199.0462	$199.05	$199.05	$199.00
7 purchase totals =	$849.05		$942.3763	$942.38	$942.35	$942.40