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	$90.80	13.698%	$103.2378	$103.24	$103.25	$103.20
Purchase #2	$248.39	13.395%	$281.6618	$281.66	$281.65	$281.70
Purchase #3	$195.49	13.706%	$222.2839	$222.28	$222.30	$222.30
Purchase #4	$211.73	13.342%	$239.979	$239.98	$240.00	$240.00
Purchase #5	$62.96	3.272%	$65.0201	$65.02	$65.00	$65.00
Purchase #6	$18.28	11.152%	$20.3186	$20.32	$20.30	$20.30
Purchase #7	$38.61	13.668%	$43.8872	$43.89	$43.90	$43.90
7 purchase totals =	$866.26		$976.3884	$976.39	$976.40	$976.40