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	$10.91	6.200%	$11.5864	$11.59	$11.60	$11.60
Purchase #2	$90.57	5.141%	$95.2262	$95.23	$95.25	$95.20
Purchase #3	$140.77	13.443%	$159.6937	$159.69	$159.70	$159.70
Purchase #4	$79.36	7.511%	$85.3207	$85.32	$85.30	$85.30
Purchase #5	$6.68	13.678%	$7.5937	$7.59	$7.60	$7.60
Purchase #6	$33.28	6.670%	$35.4998	$35.50	$35.50	$35.50
Purchase #7	$72.80	10.669%	$80.567	$80.57	$80.55	$80.60
7 purchase totals =	$434.37		$475.4875	$475.49	$475.50	$475.50