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	$108.45	13.594%	$123.1927	$123.19	$123.20	$123.20
Purchase #2	$219.38	6.759%	$234.2079	$234.21	$234.20	$234.20
Purchase #3	$172.52	12.586%	$194.2334	$194.23	$194.25	$194.20
Purchase #4	$112.48	9.803%	$123.5064	$123.51	$123.50	$123.50
Purchase #5	$114.48	13.764%	$130.237	$130.24	$130.25	$130.20
Purchase #6	$118.89	11.779%	$132.8941	$132.89	$132.90	$132.90
Purchase #7	$198.45	6.457%	$211.2639	$211.26	$211.25	$211.30
7 purchase totals =	$1,044.65		$1,149.5354	$1,149.53	$1,149.55	$1,149.50