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	$104.96	13.687%	$119.3259	$119.33	$119.35	$119.30
Purchase #2	$91.90	8.507%	$99.7179	$99.72	$99.70	$99.70
Purchase #3	$119.32	10.409%	$131.74	$131.74	$131.75	$131.70
Purchase #4	$135.28	13.664%	$153.7647	$153.76	$153.75	$153.80
Purchase #5	$150.99	10.773%	$167.2562	$167.26	$167.25	$167.30
Purchase #6	$127.76	9.155%	$139.4564	$139.46	$139.45	$139.50
Purchase #7	$154.98	7.402%	$166.4516	$166.45	$166.45	$166.50
7 purchase totals =	$885.19		$977.7127	$977.72	$977.70	$977.80