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	$42.75	6.279%	$45.4343	$45.43	$45.45	$45.40
Purchase #2	$38.94	8.397%	$42.2098	$42.21	$42.20	$42.20
Purchase #3	$111.83	8.185%	$120.9833	$120.98	$121.00	$121.00
Purchase #4	$162.31	11.364%	$180.7549	$180.75	$180.75	$180.80
Purchase #5	$174.29	3.329%	$180.0921	$180.09	$180.10	$180.10
Purchase #6	$223.56	4.539%	$233.7074	$233.71	$233.70	$233.70
Purchase #7	$85.89	12.345%	$96.4931	$96.49	$96.50	$96.50
7 purchase totals =	$839.57		$899.6749	$899.66	$899.70	$899.70