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	$18.62	11.192%	$20.704	$20.70	$20.70	$20.70
Purchase #2	$101.87	7.449%	$109.4583	$109.46	$109.45	$109.50
Purchase #3	$146.64	3.278%	$151.4469	$151.45	$151.45	$151.40
Purchase #4	$126.33	12.262%	$141.8206	$141.82	$141.80	$141.80
Purchase #5	$125.33	12.421%	$140.8972	$140.90	$140.90	$140.90
Purchase #6	$178.48	7.532%	$191.9231	$191.92	$191.90	$191.90
Purchase #7	$120.31	5.552%	$126.9896	$126.99	$127.00	$127.00
7 purchase totals =	$817.58		$883.2397	$883.24	$883.20	$883.20