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	$202.78	11.236%	$225.5644	$225.56	$225.55	$225.60
Purchase #2	$135.55	12.798%	$152.8977	$152.90	$152.90	$152.90
Purchase #3	$166.51	8.648%	$180.9098	$180.91	$180.90	$180.90
Purchase #4	$184.96	12.826%	$208.683	$208.68	$208.70	$208.70
Purchase #5	$48.37	13.126%	$54.719	$54.72	$54.70	$54.70
Purchase #6	$245.45	7.625%	$264.1656	$264.17	$264.15	$264.20
Purchase #7	$91.77	3.410%	$94.8994	$94.90	$94.90	$94.90
7 purchase totals =	$1,075.39		$1,181.8389	$1,181.84	$1,181.80	$1,181.90