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	$147.27	12.172%	$165.1957	$165.20	$165.20	$165.20
Purchase #2	$207.91	5.122%	$218.5592	$218.56	$218.55	$218.60
Purchase #3	$146.54	12.273%	$164.5249	$164.52	$164.50	$164.50
Purchase #4	$195.46	12.300%	$219.5016	$219.50	$219.50	$219.50
Purchase #5	$164.69	5.812%	$174.2618	$174.26	$174.25	$174.30
Purchase #6	$179.38	7.457%	$192.7564	$192.76	$192.75	$192.80
Purchase #7	$159.35	6.580%	$169.8352	$169.84	$169.85	$169.80
7 purchase totals =	$1,200.60		$1,304.6348	$1,304.64	$1,304.60	$1,304.70