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	$82.78	7.787%	$89.2261	$89.23	$89.25	$89.20
Purchase #2	$96.64	10.703%	$106.9834	$106.98	$107.00	$107.00
Purchase #3	$37.87	12.383%	$42.5594	$42.56	$42.55	$42.60
Purchase #4	$184.57	10.459%	$203.8742	$203.87	$203.85	$203.90
Purchase #5	$95.43	5.236%	$100.4267	$100.43	$100.45	$100.40
Purchase #6	$213.59	9.222%	$233.2873	$233.29	$233.30	$233.30
Purchase #7	$71.41	7.167%	$76.528	$76.53	$76.55	$76.50
7 purchase totals =	$782.29		$852.8851	$852.89	$852.95	$852.90