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	$28.46	10.696%	$31.5041	$31.50	$31.50	$31.50
Purchase #2	$109.87	6.399%	$116.9006	$116.90	$116.90	$116.90
Purchase #3	$77.72	5.618%	$82.0863	$82.09	$82.10	$82.10
Purchase #4	$202.75	13.399%	$229.9165	$229.92	$229.90	$229.90
Purchase #5	$99.88	4.311%	$104.1858	$104.19	$104.20	$104.20
Purchase #6	$192.76	10.424%	$212.8533	$212.85	$212.85	$212.90
Purchase #7	$99.75	10.425%	$110.1489	$110.15	$110.15	$110.10
7 purchase totals =	$811.19		$887.5955	$887.60	$887.60	$887.60