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	$15.69	12.544%	$17.6582	$17.66	$17.65	$17.70
Purchase #2	$195.82	7.322%	$210.1579	$210.16	$210.15	$210.20
Purchase #3	$98.91	13.804%	$112.5635	$112.56	$112.55	$112.60
Purchase #4	$119.54	7.645%	$128.6788	$128.68	$128.70	$128.70
Purchase #5	$77.72	7.201%	$83.3166	$83.32	$83.30	$83.30
Purchase #6	$213.96	6.538%	$227.9487	$227.95	$227.95	$227.90
Purchase #7	$56.78	4.565%	$59.372	$59.37	$59.35	$59.40
7 purchase totals =	$778.42		$839.6957	$839.70	$839.65	$839.80