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	$117.45	5.303%	$123.6784	$123.68	$123.70	$123.70
Purchase #2	$239.63	12.658%	$269.9624	$269.96	$269.95	$270.00
Purchase #3	$236.61	13.681%	$268.9806	$268.98	$269.00	$269.00
Purchase #4	$118.79	3.314%	$122.7267	$122.73	$122.75	$122.70
Purchase #5	$41.37	10.162%	$45.574	$45.57	$45.55	$45.60
Purchase #6	$238.48	7.107%	$255.4288	$255.43	$255.45	$255.40
Purchase #7	$150.83	9.695%	$165.453	$165.45	$165.45	$165.50
7 purchase totals =	$1,143.16		$1,251.8039	$1,251.80	$1,251.85	$1,251.90