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	$165.80	6.561%	$176.6781	$176.68	$176.70	$176.70
Purchase #2	$166.61	9.483%	$182.4096	$182.41	$182.40	$182.40
Purchase #3	$54.83	11.360%	$61.0587	$61.06	$61.05	$61.10
Purchase #4	$142.85	12.560%	$160.792	$160.79	$160.80	$160.80
Purchase #5	$126.34	13.568%	$143.4818	$143.48	$143.50	$143.50
Purchase #6	$225.53	13.654%	$256.3239	$256.32	$256.30	$256.30
Purchase #7	$99.94	3.465%	$103.4029	$103.40	$103.40	$103.40
7 purchase totals =	$981.90		$1,084.1470	$1,084.14	$1,084.15	$1,084.20