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	$18.86	5.275%	$19.8549	$19.85	$19.85	$19.90
Purchase #2	$167.86	9.377%	$183.6002	$183.60	$183.60	$183.60
Purchase #3	$118.91	8.286%	$128.7629	$128.76	$128.75	$128.80
Purchase #4	$200.32	11.466%	$223.2887	$223.29	$223.30	$223.30
Purchase #5	$89.35	6.185%	$94.8763	$94.88	$94.90	$94.90
Purchase #6	$237.34	11.171%	$263.8533	$263.85	$263.85	$263.90
Purchase #7	$250.66	11.432%	$279.3155	$279.32	$279.30	$279.30
7 purchase totals =	$1,083.30		$1,193.5518	$1,193.55	$1,193.55	$1,193.70