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	$73.31	7.288%	$78.6528	$78.65	$78.65	$78.70
Purchase #2	$180.97	10.457%	$199.894	$199.89	$199.90	$199.90
Purchase #3	$93.79	11.638%	$104.7053	$104.71	$104.70	$104.70
Purchase #4	$116.60	10.289%	$128.597	$128.60	$128.60	$128.60
Purchase #5	$13.91	3.279%	$14.3661	$14.37	$14.35	$14.40
Purchase #6	$88.76	6.804%	$94.7992	$94.80	$94.80	$94.80
Purchase #7	$152.75	10.439%	$168.6956	$168.70	$168.70	$168.70
7 purchase totals =	$720.09		$789.7100	$789.72	$789.70	$789.80