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	$97.77	7.298%	$104.9053	$104.91	$104.90	$104.90
Purchase #2	$59.94	12.816%	$67.6219	$67.62	$67.60	$67.60
Purchase #3	$67.45	9.334%	$73.7458	$73.75	$73.75	$73.70
Purchase #4	$78.83	3.334%	$81.4582	$81.46	$81.45	$81.50
Purchase #5	$86.28	6.156%	$91.5914	$91.59	$91.60	$91.60
Purchase #6	$198.48	5.227%	$208.8545	$208.85	$208.85	$208.90
Purchase #7	$222.99	9.243%	$243.601	$243.60	$243.60	$243.60
7 purchase totals =	$811.74		$871.7781	$871.78	$871.75	$871.80