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	$189.72	5.220%	$199.6234	$199.62	$199.60	$199.60
Purchase #2	$204.74	4.445%	$213.8407	$213.84	$213.85	$213.80
Purchase #3	$89.54	10.107%	$98.5898	$98.59	$98.60	$98.60
Purchase #4	$81.92	10.262%	$90.3266	$90.33	$90.35	$90.30
Purchase #5	$170.54	9.557%	$186.8385	$186.84	$186.85	$186.80
Purchase #6	$83.83	4.699%	$87.7692	$87.77	$87.75	$87.80
Purchase #7	$35.79	4.595%	$37.4346	$37.43	$37.45	$37.40
7 purchase totals =	$856.08		$914.4228	$914.42	$914.45	$914.30