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	$97.27	12.640%	$109.5649	$109.56	$109.55	$109.60
Purchase #2	$205.27	8.753%	$223.2373	$223.24	$223.25	$223.20
Purchase #3	$47.41	12.458%	$53.3163	$53.32	$53.30	$53.30
Purchase #4	$233.37	10.485%	$257.8388	$257.84	$257.85	$257.80
Purchase #5	$78.70	13.402%	$89.2474	$89.25	$89.25	$89.20
Purchase #6	$141.29	11.249%	$157.1837	$157.18	$157.20	$157.20
Purchase #7	$181.81	10.323%	$200.5782	$200.58	$200.60	$200.60
7 purchase totals =	$985.12		$1,090.9666	$1,090.97	$1,091.00	$1,090.90