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	$120.60	6.776%	$128.7719	$128.77	$128.75	$128.80
Purchase #2	$222.75	3.152%	$229.7711	$229.77	$229.75	$229.80
Purchase #3	$138.27	10.311%	$152.527	$152.53	$152.55	$152.50
Purchase #4	$233.36	10.133%	$257.0064	$257.01	$257.00	$257.00
Purchase #5	$70.44	3.397%	$72.8328	$72.83	$72.85	$72.80
Purchase #6	$201.54	12.413%	$226.5572	$226.56	$226.55	$226.60
Purchase #7	$169.90	10.442%	$187.641	$187.64	$187.65	$187.60
7 purchase totals =	$1,156.86		$1,255.1074	$1,255.11	$1,255.10	$1,255.10