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	$40.38	13.675%	$45.902	$45.90	$45.90	$45.90
Purchase #2	$141.76	6.150%	$150.4782	$150.48	$150.50	$150.50
Purchase #3	$103.66	5.563%	$109.4266	$109.43	$109.45	$109.40
Purchase #4	$81.46	6.162%	$86.4796	$86.48	$86.50	$86.50
Purchase #5	$15.41	8.427%	$16.7086	$16.71	$16.70	$16.70
Purchase #6	$111.63	13.631%	$126.8463	$126.85	$126.85	$126.80
Purchase #7	$143.91	3.812%	$149.3958	$149.40	$149.40	$149.40
7 purchase totals =	$638.21		$685.2371	$685.25	$685.30	$685.20