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	$108.56	10.607%	$120.075	$120.08	$120.10	$120.10
Purchase #2	$180.29	12.546%	$202.9092	$202.91	$202.90	$202.90
Purchase #3	$136.72	5.714%	$144.5322	$144.53	$144.55	$144.50
Purchase #4	$100.89	3.484%	$104.405	$104.41	$104.40	$104.40
Purchase #5	$141.94	4.709%	$148.624	$148.62	$148.60	$148.60
Purchase #6	$179.26	3.679%	$185.855	$185.86	$185.85	$185.90
Purchase #7	$190.72	8.488%	$206.9083	$206.91	$206.90	$206.90
7 purchase totals =	$1,038.38		$1,113.3087	$1,113.32	$1,113.30	$1,113.30