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	$69.35	13.274%	$78.5555	$78.56	$78.55	$78.60
Purchase #2	$204.32	4.238%	$212.9791	$212.98	$213.00	$213.00
Purchase #3	$128.83	13.472%	$146.186	$146.19	$146.20	$146.20
Purchase #4	$152.67	6.682%	$162.8714	$162.87	$162.85	$162.90
Purchase #5	$19.74	10.871%	$21.8859	$21.89	$21.90	$21.90
Purchase #6	$142.83	3.306%	$147.552	$147.55	$147.55	$147.60
Purchase #7	$81.68	12.214%	$91.6564	$91.66	$91.65	$91.70
7 purchase totals =	$799.42		$861.6863	$861.70	$861.70	$861.90