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	$81.39	9.523%	$89.1408	$89.14	$89.15	$89.10
Purchase #2	$137.75	3.501%	$142.5726	$142.57	$142.55	$142.60
Purchase #3	$182.49	8.386%	$197.7936	$197.79	$197.80	$197.80
Purchase #4	$124.89	4.811%	$130.8985	$130.90	$130.90	$130.90
Purchase #5	$231.32	5.527%	$244.1051	$244.11	$244.10	$244.10
Purchase #6	$166.66	3.360%	$172.2598	$172.26	$172.25	$172.30
Purchase #7	$174.72	11.165%	$194.2275	$194.23	$194.25	$194.20
7 purchase totals =	$1,099.22		$1,170.9979	$1,171.00	$1,171.00	$1,171.00