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	$72.72	8.613%	$78.9834	$78.98	$79.00	$79.00
Purchase #2	$246.74	3.805%	$256.1285	$256.13	$256.15	$256.10
Purchase #3	$185.84	11.314%	$206.8659	$206.87	$206.85	$206.90
Purchase #4	$188.96	6.316%	$200.8947	$200.89	$200.90	$200.90
Purchase #5	$139.71	13.290%	$158.2775	$158.28	$158.30	$158.30
Purchase #6	$103.51	12.853%	$116.8141	$116.81	$116.80	$116.80
Purchase #7	$236.97	10.120%	$260.9514	$260.95	$260.95	$261.00
7 purchase totals =	$1,174.45		$1,278.9155	$1,278.91	$1,278.95	$1,279.00