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	$19.40	12.574%	$21.8394	$21.84	$21.85	$21.80
Purchase #2	$31.33	4.291%	$32.6744	$32.67	$32.65	$32.70
Purchase #3	$136.73	3.166%	$141.0589	$141.06	$141.05	$141.10
Purchase #4	$178.33	6.408%	$189.7574	$189.76	$189.75	$189.80
Purchase #5	$98.72	13.224%	$111.7747	$111.77	$111.75	$111.80
Purchase #6	$227.37	9.634%	$249.2748	$249.27	$249.25	$249.30
Purchase #7	$33.81	12.193%	$37.9325	$37.93	$37.95	$37.90
7 purchase totals =	$725.69		$784.3121	$784.30	$784.25	$784.40