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	$40.98	4.148%	$42.6799	$42.68	$42.70	$42.70
Purchase #2	$42.37	7.436%	$45.5206	$45.52	$45.50	$45.50
Purchase #3	$204.74	13.198%	$231.7616	$231.76	$231.75	$231.80
Purchase #4	$66.44	13.724%	$75.5582	$75.56	$75.55	$75.60
Purchase #5	$96.33	4.317%	$100.4886	$100.49	$100.50	$100.50
Purchase #6	$248.71	7.447%	$267.2314	$267.23	$267.25	$267.20
Purchase #7	$245.29	13.212%	$277.6977	$277.70	$277.70	$277.70
7 purchase totals =	$944.86		$1,040.9380	$1,040.94	$1,040.95	$1,041.00