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	$243.97	5.819%	$258.1666	$258.17	$258.15	$258.20
Purchase #2	$82.80	13.323%	$93.8314	$93.83	$93.85	$93.80
Purchase #3	$119.40	7.854%	$128.7777	$128.78	$128.80	$128.80
Purchase #4	$148.70	13.182%	$168.3016	$168.30	$168.30	$168.30
Purchase #5	$199.62	11.368%	$222.3128	$222.31	$222.30	$222.30
Purchase #6	$131.47	12.121%	$147.4055	$147.41	$147.40	$147.40
Purchase #7	$162.26	6.239%	$172.3834	$172.38	$172.40	$172.40
7 purchase totals =	$1,088.22		$1,191.1790	$1,191.18	$1,191.20	$1,191.20