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	$250.86	10.469%	$277.1225	$277.12	$277.10	$277.10
Purchase #2	$39.99	8.361%	$43.3336	$43.33	$43.35	$43.30
Purchase #3	$40.83	3.751%	$42.3615	$42.36	$42.35	$42.40
Purchase #4	$170.64	10.258%	$188.1443	$188.14	$188.15	$188.10
Purchase #5	$168.27	4.364%	$175.6133	$175.61	$175.60	$175.60
Purchase #6	$198.48	12.648%	$223.5838	$223.58	$223.60	$223.60
Purchase #7	$49.79	10.480%	$55.008	$55.01	$55.00	$55.00
7 purchase totals =	$918.86		$1,005.1670	$1,005.15	$1,005.15	$1,005.10