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	$82.87	10.732%	$91.7636	$91.76	$91.75	$91.80
Purchase #2	$125.74	11.857%	$140.649	$140.65	$140.65	$140.60
Purchase #3	$92.89	13.377%	$105.3159	$105.32	$105.30	$105.30
Purchase #4	$105.61	11.428%	$117.6791	$117.68	$117.70	$117.70
Purchase #5	$181.99	7.825%	$196.2307	$196.23	$196.25	$196.20
Purchase #6	$153.57	13.647%	$174.5277	$174.53	$174.55	$174.50
Purchase #7	$154.87	7.184%	$165.9959	$166.00	$166.00	$166.00
7 purchase totals =	$897.54		$992.1619	$992.17	$992.20	$992.10