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	$86.68	3.305%	$89.5448	$89.54	$89.55	$89.50
Purchase #2	$229.71	10.512%	$253.8571	$253.86	$253.85	$253.90
Purchase #3	$225.90	10.803%	$250.304	$250.30	$250.30	$250.30
Purchase #4	$186.52	7.393%	$200.3094	$200.31	$200.30	$200.30
Purchase #5	$105.39	10.856%	$116.8311	$116.83	$116.85	$116.80
Purchase #6	$234.47	3.683%	$243.1055	$243.11	$243.10	$243.10
Purchase #7	$173.33	13.378%	$196.5181	$196.52	$196.50	$196.50
7 purchase totals =	$1,242.00		$1,350.4700	$1,350.47	$1,350.45	$1,350.40