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	$19.77	10.729%	$21.8911	$21.89	$21.90	$21.90
Purchase #2	$248.70	13.334%	$281.8617	$281.86	$281.85	$281.90
Purchase #3	$135.88	12.504%	$152.8704	$152.87	$152.85	$152.90
Purchase #4	$127.53	13.145%	$144.2938	$144.29	$144.30	$144.30
Purchase #5	$211.88	5.294%	$223.0969	$223.10	$223.10	$223.10
Purchase #6	$63.91	10.769%	$70.7925	$70.79	$70.80	$70.80
Purchase #7	$37.96	6.596%	$40.4638	$40.46	$40.45	$40.50
7 purchase totals =	$845.63		$935.2702	$935.26	$935.25	$935.40