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	$171.49	4.560%	$179.3099	$179.31	$179.30	$179.30
Purchase #2	$192.92	9.619%	$211.477	$211.48	$211.50	$211.50
Purchase #3	$116.96	10.211%	$128.9028	$128.90	$128.90	$128.90
Purchase #4	$52.37	4.748%	$54.8565	$54.86	$54.85	$54.90
Purchase #5	$71.91	5.519%	$75.8787	$75.88	$75.90	$75.90
Purchase #6	$38.59	5.623%	$40.7599	$40.76	$40.75	$40.80
Purchase #7	$174.44	5.652%	$184.2993	$184.30	$184.30	$184.30
7 purchase totals =	$818.68		$875.4841	$875.49	$875.50	$875.60