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	$48.69	13.736%	$55.3781	$55.38	$55.40	$55.40
Purchase #2	$54.96	7.482%	$59.0721	$59.07	$59.05	$59.10
Purchase #3	$21.56	7.235%	$23.1199	$23.12	$23.10	$23.10
Purchase #4	$194.83	13.717%	$221.5548	$221.55	$221.55	$221.60
Purchase #5	$154.51	7.383%	$165.9175	$165.92	$165.90	$165.90
Purchase #6	$85.53	12.207%	$95.9706	$95.97	$95.95	$96.00
Purchase #7	$197.76	12.690%	$222.8557	$222.86	$222.85	$222.90
7 purchase totals =	$757.84		$843.8687	$843.87	$843.80	$844.00