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	$249.62	6.642%	$266.1998	$266.20	$266.20	$266.20
Purchase #2	$76.34	13.465%	$86.6192	$86.62	$86.60	$86.60
Purchase #3	$77.47	7.610%	$83.3655	$83.37	$83.35	$83.40
Purchase #4	$203.95	10.415%	$225.1914	$225.19	$225.20	$225.20
Purchase #5	$41.60	4.243%	$43.3651	$43.37	$43.35	$43.40
Purchase #6	$73.54	12.306%	$82.5898	$82.59	$82.60	$82.60
Purchase #7	$188.61	4.399%	$196.907	$196.91	$196.90	$196.90
7 purchase totals =	$911.13		$984.2378	$984.25	$984.20	$984.30