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	$44.28	6.532%	$47.1724	$47.17	$47.15	$47.20
Purchase #2	$161.78	6.415%	$172.1582	$172.16	$172.15	$172.20
Purchase #3	$155.26	12.626%	$174.8631	$174.86	$174.85	$174.90
Purchase #4	$168.98	12.735%	$190.4996	$190.50	$190.50	$190.50
Purchase #5	$220.42	10.313%	$243.1519	$243.15	$243.15	$243.20
Purchase #6	$72.82	11.110%	$80.9103	$80.91	$80.90	$80.90
Purchase #7	$18.33	3.341%	$18.9424	$18.94	$18.95	$18.90
7 purchase totals =	$841.87		$927.6979	$927.69	$927.65	$927.80