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	$10.30	12.269%	$11.5637	$11.56	$11.55	$11.60
Purchase #2	$136.35	8.508%	$147.9507	$147.95	$147.95	$148.00
Purchase #3	$237.32	5.519%	$250.4177	$250.42	$250.40	$250.40
Purchase #4	$173.93	6.373%	$185.0146	$185.01	$185.00	$185.00
Purchase #5	$131.89	11.397%	$146.9215	$146.92	$146.90	$146.90
Purchase #6	$130.50	12.517%	$146.8347	$146.83	$146.85	$146.80
Purchase #7	$80.79	3.779%	$83.8431	$83.84	$83.85	$83.80
7 purchase totals =	$901.08		$972.5460	$972.53	$972.50	$972.50