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	$94.79	4.624%	$99.1731	$99.17	$99.15	$99.20
Purchase #2	$104.57	7.661%	$112.5811	$112.58	$112.60	$112.60
Purchase #3	$91.61	10.380%	$101.1191	$101.12	$101.10	$101.10
Purchase #4	$145.25	4.256%	$151.4318	$151.43	$151.45	$151.40
Purchase #5	$110.93	5.402%	$116.9224	$116.92	$116.90	$116.90
Purchase #6	$132.26	11.685%	$147.7146	$147.71	$147.70	$147.70
Purchase #7	$229.56	9.303%	$250.916	$250.92	$250.90	$250.90
7 purchase totals =	$908.97		$979.8581	$979.85	$979.80	$979.80