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	$82.35	9.380%	$90.0744	$90.07	$90.05	$90.10
Purchase #2	$248.68	9.625%	$272.6155	$272.62	$272.60	$272.60
Purchase #3	$76.39	12.363%	$85.8341	$85.83	$85.85	$85.80
Purchase #4	$206.34	3.508%	$213.5784	$213.58	$213.60	$213.60
Purchase #5	$131.81	4.425%	$137.6426	$137.64	$137.65	$137.60
Purchase #6	$58.41	12.402%	$65.654	$65.65	$65.65	$65.70
Purchase #7	$169.64	11.721%	$189.5235	$189.52	$189.50	$189.50
7 purchase totals =	$973.62		$1,054.9225	$1,054.91	$1,054.90	$1,054.90