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	$66.66	5.782%	$70.5143	$70.51	$70.50	$70.50
Purchase #2	$13.39	5.667%	$14.1488	$14.15	$14.15	$14.10
Purchase #3	$202.91	10.818%	$224.8608	$224.86	$224.85	$224.90
Purchase #4	$54.36	8.637%	$59.0551	$59.06	$59.05	$59.10
Purchase #5	$6.77	5.399%	$7.1355	$7.14	$7.15	$7.10
Purchase #6	$125.26	6.513%	$133.4182	$133.42	$133.40	$133.40
Purchase #7	$64.83	12.465%	$72.9111	$72.91	$72.90	$72.90
7 purchase totals =	$534.18		$582.0438	$582.05	$582.00	$582.00