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	$6.61	13.597%	$7.5088	$7.51	$7.50	$7.50
Purchase #2	$222.34	9.360%	$243.151	$243.15	$243.15	$243.20
Purchase #3	$45.97	6.354%	$48.8909	$48.89	$48.90	$48.90
Purchase #4	$150.61	10.784%	$166.8518	$166.85	$166.85	$166.90
Purchase #5	$77.87	10.744%	$86.2364	$86.24	$86.25	$86.20
Purchase #6	$128.46	12.411%	$144.4032	$144.40	$144.40	$144.40
Purchase #7	$226.86	10.375%	$250.3967	$250.40	$250.40	$250.40
7 purchase totals =	$858.72		$947.4388	$947.44	$947.45	$947.50