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	$163.56	9.736%	$179.4842	$179.48	$179.50	$179.50
Purchase #2	$145.89	8.142%	$157.7684	$157.77	$157.75	$157.80
Purchase #3	$70.98	11.647%	$79.247	$79.25	$79.25	$79.20
Purchase #4	$35.63	9.141%	$38.8869	$38.89	$38.90	$38.90
Purchase #5	$173.86	10.704%	$192.47	$192.47	$192.45	$192.50
Purchase #6	$41.73	3.626%	$43.2431	$43.24	$43.25	$43.20
Purchase #7	$137.84	6.132%	$146.2923	$146.29	$146.30	$146.30
7 purchase totals =	$769.49		$837.3919	$837.39	$837.40	$837.40