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	$205.92	6.288%	$218.8682	$218.87	$218.85	$218.90
Purchase #2	$84.92	8.103%	$91.8011	$91.80	$91.80	$91.80
Purchase #3	$204.27	8.746%	$222.1355	$222.14	$222.15	$222.10
Purchase #4	$16.77	9.825%	$18.4177	$18.42	$18.40	$18.40
Purchase #5	$92.96	9.487%	$101.7791	$101.78	$101.80	$101.80
Purchase #6	$64.56	11.215%	$71.8004	$71.80	$71.80	$71.80
Purchase #7	$80.33	10.219%	$88.5389	$88.54	$88.55	$88.50
7 purchase totals =	$749.73		$813.3409	$813.35	$813.35	$813.30