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	$98.86	4.288%	$103.0991	$103.10	$103.10	$103.10
Purchase #2	$82.47	7.205%	$88.412	$88.41	$88.40	$88.40
Purchase #3	$18.77	13.209%	$21.2493	$21.25	$21.25	$21.20
Purchase #4	$22.41	10.544%	$24.7729	$24.77	$24.75	$24.80
Purchase #5	$158.42	4.387%	$165.3699	$165.37	$165.35	$165.40
Purchase #6	$211.48	10.564%	$233.8207	$233.82	$233.80	$233.80
Purchase #7	$187.29	11.689%	$209.1823	$209.18	$209.20	$209.20
7 purchase totals =	$779.70		$845.9062	$845.90	$845.85	$845.90