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	$157.36	3.259%	$162.4884	$162.49	$162.50	$162.50
Purchase #2	$229.76	4.823%	$240.8413	$240.84	$240.85	$240.80
Purchase #3	$135.27	11.872%	$151.3293	$151.33	$151.35	$151.30
Purchase #4	$61.59	8.576%	$66.872	$66.87	$66.85	$66.90
Purchase #5	$168.36	4.711%	$176.2914	$176.29	$176.30	$176.30
Purchase #6	$126.55	13.392%	$143.4976	$143.50	$143.50	$143.50
Purchase #7	$141.98	3.414%	$146.8272	$146.83	$146.85	$146.80
7 purchase totals =	$1,020.87		$1,088.1472	$1,088.15	$1,088.20	$1,088.10