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	$98.46	11.622%	$109.903	$109.90	$109.90	$109.90
Purchase #2	$46.56	3.697%	$48.2813	$48.28	$48.30	$48.30
Purchase #3	$121.36	7.626%	$130.6149	$130.61	$130.60	$130.60
Purchase #4	$174.85	3.424%	$180.8369	$180.84	$180.85	$180.80
Purchase #5	$83.73	6.421%	$89.1063	$89.11	$89.10	$89.10
Purchase #6	$121.91	13.407%	$138.2545	$138.25	$138.25	$138.30
Purchase #7	$231.29	12.110%	$259.2992	$259.30	$259.30	$259.30
7 purchase totals =	$878.16		$956.2961	$956.29	$956.30	$956.30