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	$171.28	6.310%	$182.0878	$182.09	$182.10	$182.10
Purchase #2	$115.59	11.384%	$128.7488	$128.75	$128.75	$128.70
Purchase #3	$244.38	8.402%	$264.9128	$264.91	$264.90	$264.90
Purchase #4	$122.63	6.414%	$130.4955	$130.50	$130.50	$130.50
Purchase #5	$85.79	4.594%	$89.7312	$89.73	$89.75	$89.70
Purchase #6	$141.88	8.343%	$153.717	$153.72	$153.70	$153.70
Purchase #7	$216.73	8.705%	$235.5963	$235.60	$235.60	$235.60
7 purchase totals =	$1,098.28		$1,185.2894	$1,185.30	$1,185.30	$1,185.20