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	$60.76	13.208%	$68.7852	$68.79	$68.80	$68.80
Purchase #2	$132.27	6.832%	$141.3067	$141.31	$141.30	$141.30
Purchase #3	$39.39	8.691%	$42.8134	$42.81	$42.80	$42.80
Purchase #4	$37.56	12.530%	$42.2663	$42.27	$42.25	$42.30
Purchase #5	$77.88	6.319%	$82.8012	$82.80	$82.80	$82.80
Purchase #6	$68.60	4.445%	$71.6493	$71.65	$71.65	$71.60
Purchase #7	$250.31	10.226%	$275.9067	$275.91	$275.90	$275.90
7 purchase totals =	$666.77		$725.5288	$725.54	$725.50	$725.50