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	$110.72	8.417%	$120.0393	$120.04	$120.05	$120.00
Purchase #2	$174.52	12.369%	$196.1064	$196.11	$196.10	$196.10
Purchase #3	$53.46	6.712%	$57.0482	$57.05	$57.05	$57.00
Purchase #4	$249.83	11.728%	$279.1301	$279.13	$279.15	$279.10
Purchase #5	$154.37	9.189%	$168.5551	$168.56	$168.55	$168.60
Purchase #6	$163.63	11.143%	$181.8633	$181.86	$181.85	$181.90
Purchase #7	$84.47	12.694%	$95.1926	$95.19	$95.20	$95.20
7 purchase totals =	$991.00		$1,097.9350	$1,097.94	$1,097.95	$1,097.90