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	$122.74	7.473%	$131.9124	$131.91	$131.90	$131.90
Purchase #2	$152.87	10.241%	$168.5254	$168.53	$168.55	$168.50
Purchase #3	$214.64	6.829%	$229.2978	$229.30	$229.30	$229.30
Purchase #4	$119.91	11.428%	$133.6133	$133.61	$133.60	$133.60
Purchase #5	$221.76	4.652%	$232.0763	$232.08	$232.10	$232.10
Purchase #6	$158.56	5.133%	$166.6989	$166.70	$166.70	$166.70
Purchase #7	$82.59	9.802%	$90.6855	$90.69	$90.70	$90.70
7 purchase totals =	$1,073.07		$1,152.8096	$1,152.82	$1,152.85	$1,152.80