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	$50.83	5.631%	$53.6922	$53.69	$53.70	$53.70
Purchase #2	$165.65	11.216%	$184.2293	$184.23	$184.25	$184.20
Purchase #3	$13.84	12.374%	$15.5526	$15.55	$15.55	$15.60
Purchase #4	$97.88	6.414%	$104.158	$104.16	$104.15	$104.20
Purchase #5	$245.34	7.735%	$264.317	$264.32	$264.30	$264.30
Purchase #6	$74.36	10.333%	$82.0436	$82.04	$82.05	$82.00
Purchase #7	$142.41	13.383%	$161.4687	$161.47	$161.45	$161.50
7 purchase totals =	$790.31		$865.4614	$865.46	$865.45	$865.50