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	$34.61	6.260%	$36.7766	$36.78	$36.80	$36.80
Purchase #2	$25.69	10.760%	$28.4542	$28.45	$28.45	$28.50
Purchase #3	$242.44	13.478%	$275.1161	$275.12	$275.10	$275.10
Purchase #4	$250.70	11.382%	$279.2347	$279.23	$279.25	$279.20
Purchase #5	$80.70	11.355%	$89.8635	$89.86	$89.85	$89.90
Purchase #6	$229.60	13.679%	$261.007	$261.01	$261.00	$261.00
Purchase #7	$97.70	3.306%	$100.93	$100.93	$100.95	$100.90
7 purchase totals =	$961.44		$1,071.3821	$1,071.38	$1,071.40	$1,071.40