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	$233.32	4.280%	$243.3061	$243.31	$243.30	$243.30
Purchase #2	$129.44	13.288%	$146.64	$146.64	$146.65	$146.60
Purchase #3	$57.71	6.854%	$61.6654	$61.67	$61.65	$61.70
Purchase #4	$59.66	10.630%	$66.0019	$66.00	$66.00	$66.00
Purchase #5	$119.43	7.647%	$128.5628	$128.56	$128.55	$128.60
Purchase #6	$7.48	4.615%	$7.8252	$7.83	$7.85	$7.80
Purchase #7	$37.61	4.451%	$39.284	$39.28	$39.30	$39.30
7 purchase totals =	$644.65		$693.2854	$693.29	$693.30	$693.30