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	$28.99	9.729%	$31.8104	$31.81	$31.80	$31.80
Purchase #2	$219.89	12.484%	$247.3411	$247.34	$247.35	$247.30
Purchase #3	$185.92	13.268%	$210.5879	$210.59	$210.60	$210.60
Purchase #4	$146.77	3.814%	$152.3678	$152.37	$152.35	$152.40
Purchase #5	$58.93	12.284%	$66.169	$66.17	$66.15	$66.20
Purchase #6	$126.62	8.763%	$137.7157	$137.72	$137.70	$137.70
Purchase #7	$174.75	12.483%	$196.564	$196.56	$196.55	$196.60
7 purchase totals =	$941.87		$1,042.5559	$1,042.56	$1,042.50	$1,042.60