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	$248.87	3.805%	$258.3395	$258.34	$258.35	$258.30
Purchase #2	$204.93	11.222%	$227.9272	$227.93	$227.95	$227.90
Purchase #3	$89.41	5.720%	$94.5243	$94.52	$94.50	$94.50
Purchase #4	$30.46	11.140%	$33.8532	$33.85	$33.85	$33.90
Purchase #5	$5.56	5.473%	$5.8643	$5.86	$5.85	$5.90
Purchase #6	$100.67	4.617%	$105.3179	$105.32	$105.30	$105.30
Purchase #7	$123.32	7.644%	$132.7466	$132.75	$132.75	$132.70
7 purchase totals =	$803.22		$858.5730	$858.57	$858.55	$858.50