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	$199.67	13.428%	$226.4817	$226.48	$226.50	$226.50
Purchase #2	$141.25	3.379%	$146.0228	$146.02	$146.00	$146.00
Purchase #3	$233.52	6.870%	$249.5628	$249.56	$249.55	$249.60
Purchase #4	$116.52	10.588%	$128.8571	$128.86	$128.85	$128.90
Purchase #5	$118.94	13.108%	$134.5307	$134.53	$134.55	$134.50
Purchase #6	$189.78	12.559%	$213.6145	$213.61	$213.60	$213.60
Purchase #7	$148.28	12.564%	$166.9099	$166.91	$166.90	$166.90
7 purchase totals =	$1,147.96		$1,265.9795	$1,265.97	$1,265.95	$1,266.00