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	$29.50	10.207%	$32.5111	$32.51	$32.50	$32.50
Purchase #2	$88.76	5.265%	$93.4332	$93.43	$93.45	$93.40
Purchase #3	$24.93	6.664%	$26.5913	$26.59	$26.60	$26.60
Purchase #4	$83.71	8.582%	$90.894	$90.89	$90.90	$90.90
Purchase #5	$244.50	4.107%	$254.5416	$254.54	$254.55	$254.50
Purchase #6	$109.68	12.682%	$123.5896	$123.59	$123.60	$123.60
Purchase #7	$83.47	9.417%	$91.3304	$91.33	$91.35	$91.30
7 purchase totals =	$664.55		$712.8912	$712.88	$712.95	$712.80