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	$57.46	5.369%	$60.545	$60.55	$60.55	$60.50
Purchase #2	$148.82	9.448%	$162.8805	$162.88	$162.90	$162.90
Purchase #3	$191.92	7.107%	$205.5598	$205.56	$205.55	$205.60
Purchase #4	$79.50	13.186%	$89.9829	$89.98	$90.00	$90.00
Purchase #5	$152.33	10.711%	$168.6461	$168.65	$168.65	$168.60
Purchase #6	$118.80	3.816%	$123.3334	$123.33	$123.35	$123.30
Purchase #7	$223.92	3.340%	$231.3989	$231.40	$231.40	$231.40
7 purchase totals =	$972.75		$1,042.3466	$1,042.35	$1,042.40	$1,042.30