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	$81.27	12.638%	$91.5409	$91.54	$91.55	$91.50
Purchase #2	$118.66	9.817%	$130.3089	$130.31	$130.30	$130.30
Purchase #3	$200.57	11.358%	$223.3507	$223.35	$223.35	$223.40
Purchase #4	$8.65	4.570%	$9.0453	$9.05	$9.05	$9.00
Purchase #5	$64.83	10.713%	$71.7752	$71.78	$71.80	$71.80
Purchase #6	$137.93	4.612%	$144.2913	$144.29	$144.30	$144.30
Purchase #7	$156.75	10.710%	$173.5379	$173.54	$173.55	$173.50
7 purchase totals =	$768.66		$843.8502	$843.86	$843.90	$843.80