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	$76.26	3.448%	$78.8894	$78.89	$78.90	$78.90
Purchase #2	$99.33	10.362%	$109.6226	$109.62	$109.60	$109.60
Purchase #3	$135.79	9.153%	$148.2189	$148.22	$148.20	$148.20
Purchase #4	$135.51	12.195%	$152.0354	$152.04	$152.05	$152.00
Purchase #5	$140.30	13.402%	$159.103	$159.10	$159.10	$159.10
Purchase #6	$87.82	11.780%	$98.1652	$98.17	$98.15	$98.20
Purchase #7	$207.99	12.266%	$233.5021	$233.50	$233.50	$233.50
7 purchase totals =	$883.00		$979.5366	$979.54	$979.50	$979.50