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	$80.66	13.284%	$91.3749	$91.37	$91.35	$91.40
Purchase #2	$61.83	9.575%	$67.7502	$67.75	$67.75	$67.80
Purchase #3	$85.95	11.443%	$95.7853	$95.79	$95.80	$95.80
Purchase #4	$108.54	10.693%	$120.1462	$120.15	$120.15	$120.10
Purchase #5	$163.62	5.557%	$172.7124	$172.71	$172.70	$172.70
Purchase #6	$105.80	3.868%	$109.8923	$109.89	$109.90	$109.90
Purchase #7	$178.67	6.144%	$189.6475	$189.65	$189.65	$189.60
7 purchase totals =	$785.07		$847.3088	$847.31	$847.30	$847.30