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	$24.91	4.204%	$25.9572	$25.96	$25.95	$26.00
Purchase #2	$153.48	5.120%	$161.3382	$161.34	$161.35	$161.30
Purchase #3	$85.59	10.791%	$94.826	$94.83	$94.85	$94.80
Purchase #4	$46.50	8.809%	$50.5962	$50.60	$50.60	$50.60
Purchase #5	$80.33	11.171%	$89.3037	$89.30	$89.30	$89.30
Purchase #6	$90.70	8.609%	$98.5084	$98.51	$98.50	$98.50
Purchase #7	$110.73	8.222%	$119.8342	$119.83	$119.85	$119.80
7 purchase totals =	$592.24		$640.3639	$640.37	$640.40	$640.30