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	$22.61	13.250%	$25.6058	$25.61	$25.60	$25.60
Purchase #2	$113.63	8.483%	$123.2692	$123.27	$123.25	$123.30
Purchase #3	$197.86	12.833%	$223.2514	$223.25	$223.25	$223.30
Purchase #4	$112.90	8.127%	$122.0754	$122.08	$122.10	$122.10
Purchase #5	$53.52	4.616%	$55.9905	$55.99	$56.00	$56.00
Purchase #6	$172.74	10.850%	$191.4823	$191.48	$191.50	$191.50
Purchase #7	$126.38	8.657%	$137.3207	$137.32	$137.30	$137.30
7 purchase totals =	$799.64		$878.9953	$879.00	$879.00	$879.10