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	$131.87	9.586%	$144.5111	$144.51	$144.50	$144.50
Purchase #2	$78.93	7.435%	$84.7984	$84.80	$84.80	$84.80
Purchase #3	$77.49	10.388%	$85.5397	$85.54	$85.55	$85.50
Purchase #4	$142.28	11.606%	$158.793	$158.79	$158.80	$158.80
Purchase #5	$143.82	12.755%	$162.1642	$162.16	$162.15	$162.20
Purchase #6	$88.39	6.778%	$94.3811	$94.38	$94.40	$94.40
Purchase #7	$226.76	7.499%	$243.7647	$243.76	$243.75	$243.80
7 purchase totals =	$889.54		$973.9522	$973.94	$973.95	$974.00