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	$245.68	5.130%	$258.2834	$258.28	$258.30	$258.30
Purchase #2	$166.69	10.537%	$184.2541	$184.25	$184.25	$184.30
Purchase #3	$216.25	12.650%	$243.6056	$243.61	$243.60	$243.60
Purchase #4	$94.87	4.594%	$99.2283	$99.23	$99.25	$99.20
Purchase #5	$46.57	8.361%	$50.4637	$50.46	$50.45	$50.50
Purchase #6	$52.41	4.128%	$54.5735	$54.57	$54.55	$54.60
Purchase #7	$80.91	12.415%	$90.955	$90.96	$90.95	$91.00
7 purchase totals =	$903.38		$981.3636	$981.36	$981.35	$981.50