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	$131.29	12.483%	$147.6789	$147.68	$147.70	$147.70
Purchase #2	$224.78	11.614%	$250.8859	$250.89	$250.90	$250.90
Purchase #3	$234.41	3.664%	$242.9988	$243.00	$243.00	$243.00
Purchase #4	$45.78	11.223%	$50.9179	$50.92	$50.90	$50.90
Purchase #5	$28.96	8.357%	$31.3802	$31.38	$31.40	$31.40
Purchase #6	$106.76	4.136%	$111.1756	$111.18	$111.20	$111.20
Purchase #7	$8.78	7.645%	$9.4512	$9.45	$9.45	$9.50
7 purchase totals =	$780.76		$844.4885	$844.50	$844.55	$844.60