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	$144.33	10.495%	$159.4774	$159.48	$159.50	$159.50
Purchase #2	$34.61	6.654%	$36.9129	$36.91	$36.90	$36.90
Purchase #3	$211.49	10.428%	$233.5442	$233.54	$233.55	$233.50
Purchase #4	$110.34	5.593%	$116.5113	$116.51	$116.50	$116.50
Purchase #5	$117.45	11.542%	$131.0061	$131.01	$131.00	$131.00
Purchase #6	$162.55	3.594%	$168.392	$168.39	$168.40	$168.40
Purchase #7	$82.82	10.374%	$91.4117	$91.41	$91.40	$91.40
7 purchase totals =	$863.59		$937.2556	$937.25	$937.25	$937.20