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	$131.59	4.111%	$136.9997	$137.00	$137.00	$137.00
Purchase #2	$103.32	6.297%	$109.8261	$109.83	$109.85	$109.80
Purchase #3	$195.34	10.543%	$215.9347	$215.93	$215.95	$215.90
Purchase #4	$81.35	9.763%	$89.2922	$89.29	$89.30	$89.30
Purchase #5	$6.63	12.306%	$7.4459	$7.45	$7.45	$7.40
Purchase #6	$124.31	6.713%	$132.6549	$132.65	$132.65	$132.70
Purchase #7	$63.50	11.668%	$70.9092	$70.91	$70.90	$70.90
7 purchase totals =	$706.04		$763.0627	$763.06	$763.10	$763.00