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	$10.64	3.380%	$10.9996	$11.00	$11.00	$11.00
Purchase #2	$235.76	6.332%	$250.6883	$250.69	$250.70	$250.70
Purchase #3	$92.71	7.761%	$99.9052	$99.91	$99.90	$99.90
Purchase #4	$36.53	6.280%	$38.8241	$38.82	$38.80	$38.80
Purchase #5	$78.29	10.244%	$86.31	$86.31	$86.30	$86.30
Purchase #6	$134.82	6.828%	$144.0255	$144.03	$144.05	$144.00
Purchase #7	$34.46	3.821%	$35.7767	$35.78	$35.80	$35.80
7 purchase totals =	$623.21		$666.5294	$666.54	$666.55	$666.50