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	$137.56	4.358%	$143.5549	$143.55	$143.55	$143.60
Purchase #2	$12.33	4.353%	$12.8667	$12.87	$12.85	$12.90
Purchase #3	$120.34	8.363%	$130.404	$130.40	$130.40	$130.40
Purchase #4	$18.54	13.246%	$20.9958	$21.00	$21.00	$21.00
Purchase #5	$175.46	6.511%	$186.8842	$186.88	$186.90	$186.90
Purchase #6	$6.99	9.524%	$7.6557	$7.66	$7.65	$7.70
Purchase #7	$79.97	3.200%	$82.529	$82.53	$82.55	$82.50
7 purchase totals =	$551.19		$584.8903	$584.89	$584.90	$585.00