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	$99.87	4.810%	$104.6737	$104.67	$104.65	$104.70
Purchase #2	$136.46	13.787%	$155.2737	$155.27	$155.25	$155.30
Purchase #3	$149.52	10.568%	$165.3213	$165.32	$165.30	$165.30
Purchase #4	$27.56	3.693%	$28.5778	$28.58	$28.60	$28.60
Purchase #5	$103.36	6.442%	$110.0185	$110.02	$110.00	$110.00
Purchase #6	$91.83	5.161%	$96.5693	$96.57	$96.55	$96.60
Purchase #7	$162.41	10.127%	$178.8573	$178.86	$178.85	$178.90
7 purchase totals =	$771.01		$839.2916	$839.29	$839.20	$839.40