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	$37.33	13.820%	$42.489	$42.49	$42.50	$42.50
Purchase #2	$119.54	11.438%	$133.213	$133.21	$133.20	$133.20
Purchase #3	$99.35	3.198%	$102.5272	$102.53	$102.55	$102.50
Purchase #4	$117.78	8.861%	$128.2165	$128.22	$128.20	$128.20
Purchase #5	$199.50	4.837%	$209.1498	$209.15	$209.15	$209.10
Purchase #6	$13.75	3.611%	$14.2465	$14.25	$14.25	$14.20
Purchase #7	$79.64	11.300%	$88.6393	$88.64	$88.65	$88.60
7 purchase totals =	$666.89		$718.4813	$718.49	$718.50	$718.30