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	$9.65	11.471%	$10.757	$10.76	$10.75	$10.80
Purchase #2	$102.78	9.324%	$112.3632	$112.36	$112.35	$112.40
Purchase #3	$115.29	4.632%	$120.6302	$120.63	$120.65	$120.60
Purchase #4	$143.64	11.781%	$160.5622	$160.56	$160.55	$160.60
Purchase #5	$19.41	8.694%	$21.0975	$21.10	$21.10	$21.10
Purchase #6	$73.38	12.198%	$82.3309	$82.33	$82.35	$82.30
Purchase #7	$24.25	12.862%	$27.369	$27.37	$27.35	$27.40
7 purchase totals =	$488.40		$535.1100	$535.11	$535.10	$535.20