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	$75.98	6.130%	$80.6376	$80.64	$80.65	$80.60
Purchase #2	$243.96	5.200%	$256.6459	$256.65	$256.65	$256.60
Purchase #3	$88.66	4.300%	$92.4724	$92.47	$92.45	$92.50
Purchase #4	$161.51	6.244%	$171.5947	$171.59	$171.60	$171.60
Purchase #5	$58.77	10.612%	$65.0067	$65.01	$65.00	$65.00
Purchase #6	$23.54	5.769%	$24.898	$24.90	$24.90	$24.90
Purchase #7	$56.33	5.425%	$59.3859	$59.39	$59.40	$59.40
7 purchase totals =	$708.75		$750.6412	$750.65	$750.65	$750.60