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	$151.32	11.395%	$168.5629	$168.56	$168.55	$168.60
Purchase #2	$91.83	8.258%	$99.4133	$99.41	$99.40	$99.40
Purchase #3	$95.63	10.597%	$105.7639	$105.76	$105.75	$105.80
Purchase #4	$120.51	8.552%	$130.816	$130.82	$130.80	$130.80
Purchase #5	$224.49	13.555%	$254.9196	$254.92	$254.90	$254.90
Purchase #6	$24.75	10.462%	$27.3393	$27.34	$27.35	$27.30
Purchase #7	$88.96	8.493%	$96.5154	$96.52	$96.50	$96.50
7 purchase totals =	$797.49		$883.3304	$883.33	$883.25	$883.30