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	$78.71	3.624%	$81.5625	$81.56	$81.55	$81.60
Purchase #2	$172.59	4.473%	$180.31	$180.31	$180.30	$180.30
Purchase #3	$69.76	4.272%	$72.7401	$72.74	$72.75	$72.70
Purchase #4	$149.94	8.426%	$162.5739	$162.57	$162.55	$162.60
Purchase #5	$97.32	3.183%	$100.4177	$100.42	$100.40	$100.40
Purchase #6	$235.70	4.807%	$247.0301	$247.03	$247.05	$247.00
Purchase #7	$137.75	7.666%	$148.3099	$148.31	$148.30	$148.30
7 purchase totals =	$941.77		$992.9442	$992.94	$992.90	$992.90