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	$240.39	5.623%	$253.9071	$253.91	$253.90	$253.90
Purchase #2	$79.91	3.225%	$82.4871	$82.49	$82.50	$82.50
Purchase #3	$98.85	6.142%	$104.9214	$104.92	$104.90	$104.90
Purchase #4	$163.87	7.271%	$175.785	$175.79	$175.80	$175.80
Purchase #5	$126.79	13.521%	$143.9333	$143.93	$143.95	$143.90
Purchase #6	$106.74	3.313%	$110.2763	$110.28	$110.30	$110.30
Purchase #7	$179.89	5.379%	$189.5663	$189.57	$189.55	$189.60
7 purchase totals =	$996.44		$1,060.8765	$1,060.89	$1,060.90	$1,060.90