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	$249.58	11.128%	$277.3533	$277.35	$277.35	$277.40
Purchase #2	$247.91	11.238%	$275.7701	$275.77	$275.75	$275.80
Purchase #3	$74.76	3.749%	$77.5628	$77.56	$77.55	$77.60
Purchase #4	$152.42	3.440%	$157.6632	$157.66	$157.65	$157.70
Purchase #5	$83.89	6.799%	$89.5937	$89.59	$89.60	$89.60
Purchase #6	$31.36	13.381%	$35.5563	$35.56	$35.55	$35.60
Purchase #7	$75.68	9.656%	$82.9877	$82.99	$83.00	$83.00
7 purchase totals =	$915.60		$996.4871	$996.48	$996.45	$996.70