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	$202.57	6.396%	$215.5264	$215.53	$215.55	$215.50
Purchase #2	$30.72	4.227%	$32.0185	$32.02	$32.00	$32.00
Purchase #3	$118.77	7.735%	$127.9569	$127.96	$127.95	$128.00
Purchase #4	$240.62	4.144%	$250.5913	$250.59	$250.60	$250.60
Purchase #5	$135.99	4.516%	$142.1313	$142.13	$142.15	$142.10
Purchase #6	$88.67	9.237%	$96.8604	$96.86	$96.85	$96.90
Purchase #7	$12.95	3.320%	$13.3799	$13.38	$13.40	$13.40
7 purchase totals =	$830.29		$878.4647	$878.47	$878.50	$878.50