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	$58.67	13.418%	$66.5423	$66.54	$66.55	$66.50
Purchase #2	$129.90	11.538%	$144.8879	$144.89	$144.90	$144.90
Purchase #3	$33.76	11.661%	$37.6968	$37.70	$37.70	$37.70
Purchase #4	$40.57	4.298%	$42.3137	$42.31	$42.30	$42.30
Purchase #5	$203.55	6.207%	$216.1843	$216.18	$216.20	$216.20
Purchase #6	$203.98	10.664%	$225.7324	$225.73	$225.75	$225.70
Purchase #7	$242.88	11.542%	$270.9132	$270.91	$270.90	$270.90
7 purchase totals =	$913.31		$1,004.2706	$1,004.26	$1,004.30	$1,004.20