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	$26.70	6.685%	$28.4849	$28.48	$28.50	$28.50
Purchase #2	$213.64	6.559%	$227.6526	$227.65	$227.65	$227.70
Purchase #3	$178.98	7.123%	$191.7287	$191.73	$191.75	$191.70
Purchase #4	$129.95	3.408%	$134.3787	$134.38	$134.40	$134.40
Purchase #5	$83.69	8.176%	$90.5325	$90.53	$90.55	$90.50
Purchase #6	$79.70	13.278%	$90.2826	$90.28	$90.30	$90.30
Purchase #7	$225.35	7.676%	$242.6479	$242.65	$242.65	$242.60
7 purchase totals =	$938.01		$1,005.7079	$1,005.70	$1,005.80	$1,005.70