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	$79.89	13.656%	$90.7998	$90.80	$90.80	$90.80
Purchase #2	$225.99	6.732%	$241.2036	$241.20	$241.20	$241.20
Purchase #3	$114.78	3.488%	$118.7835	$118.78	$118.80	$118.80
Purchase #4	$30.39	13.582%	$34.5176	$34.52	$34.50	$34.50
Purchase #5	$98.34	11.761%	$109.9058	$109.91	$109.90	$109.90
Purchase #6	$37.88	4.765%	$39.685	$39.69	$39.70	$39.70
Purchase #7	$113.63	6.620%	$121.1523	$121.15	$121.15	$121.20
7 purchase totals =	$700.90		$756.0476	$756.05	$756.05	$756.10