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	$142.83	7.557%	$153.6237	$153.62	$153.60	$153.60
Purchase #2	$52.32	11.780%	$58.4833	$58.48	$58.50	$58.50
Purchase #3	$150.98	11.287%	$168.0211	$168.02	$168.00	$168.00
Purchase #4	$72.56	7.804%	$78.2226	$78.22	$78.20	$78.20
Purchase #5	$211.60	9.288%	$231.2534	$231.25	$231.25	$231.30
Purchase #6	$60.51	11.717%	$67.6	$67.60	$67.60	$67.60
Purchase #7	$202.88	10.481%	$224.1439	$224.14	$224.15	$224.10
7 purchase totals =	$893.68		$981.3480	$981.33	$981.30	$981.30