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	$199.51	12.377%	$224.2034	$224.20	$224.20	$224.20
Purchase #2	$120.26	8.465%	$130.44	$130.44	$130.45	$130.40
Purchase #3	$236.64	8.322%	$256.3332	$256.33	$256.35	$256.30
Purchase #4	$78.34	5.685%	$82.7936	$82.79	$82.80	$82.80
Purchase #5	$80.88	13.321%	$91.654	$91.65	$91.65	$91.70
Purchase #6	$203.53	7.255%	$218.2961	$218.30	$218.30	$218.30
Purchase #7	$55.30	11.713%	$61.7773	$61.78	$61.80	$61.80
7 purchase totals =	$974.46		$1,065.4976	$1,065.49	$1,065.55	$1,065.50