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	$88.57	12.228%	$99.4003	$99.40	$99.40	$99.40
Purchase #2	$157.36	4.254%	$164.0541	$164.05	$164.05	$164.10
Purchase #3	$75.80	12.395%	$85.1954	$85.20	$85.20	$85.20
Purchase #4	$243.34	11.274%	$270.7742	$270.77	$270.75	$270.80
Purchase #5	$159.38	12.499%	$179.3009	$179.30	$179.30	$179.30
Purchase #6	$104.34	12.686%	$117.5766	$117.58	$117.60	$117.60
Purchase #7	$154.92	7.416%	$166.4089	$166.41	$166.40	$166.40
7 purchase totals =	$983.71		$1,082.7104	$1,082.71	$1,082.70	$1,082.80