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	$101.48	3.753%	$105.2885	$105.29	$105.30	$105.30
Purchase #2	$93.34	7.671%	$100.5001	$100.50	$100.50	$100.50
Purchase #3	$86.48	3.156%	$89.2093	$89.21	$89.20	$89.20
Purchase #4	$40.32	12.601%	$45.4007	$45.40	$45.40	$45.40
Purchase #5	$108.73	10.121%	$119.7346	$119.73	$119.75	$119.70
Purchase #6	$68.54	12.495%	$77.1041	$77.10	$77.10	$77.10
Purchase #7	$217.66	13.674%	$247.4228	$247.42	$247.40	$247.40
7 purchase totals =	$716.55		$784.6601	$784.65	$784.65	$784.60