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	$186.78	6.163%	$198.2913	$198.29	$198.30	$198.30
Purchase #2	$145.89	11.233%	$162.2778	$162.28	$162.30	$162.30
Purchase #3	$40.87	10.310%	$45.0837	$45.08	$45.10	$45.10
Purchase #4	$102.84	9.505%	$112.6149	$112.61	$112.60	$112.60
Purchase #5	$168.89	12.191%	$189.4794	$189.48	$189.50	$189.50
Purchase #6	$6.68	13.347%	$7.5716	$7.57	$7.55	$7.60
Purchase #7	$121.82	9.132%	$132.9446	$132.94	$132.95	$132.90
7 purchase totals =	$773.77		$848.2633	$848.25	$848.30	$848.30