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	$49.40	4.765%	$51.7539	$51.75	$51.75	$51.80
Purchase #2	$98.84	13.248%	$111.9343	$111.93	$111.95	$111.90
Purchase #3	$172.43	13.790%	$196.2081	$196.21	$196.20	$196.20
Purchase #4	$82.48	5.288%	$86.8415	$86.84	$86.85	$86.80
Purchase #5	$166.80	7.431%	$179.1949	$179.19	$179.20	$179.20
Purchase #6	$100.68	7.369%	$108.0991	$108.10	$108.10	$108.10
Purchase #7	$158.66	12.350%	$178.2545	$178.25	$178.25	$178.30
7 purchase totals =	$829.29		$912.2863	$912.27	$912.30	$912.30