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	$188.83	11.662%	$210.8514	$210.85	$210.85	$210.90
Purchase #2	$191.50	4.563%	$200.2381	$200.24	$200.25	$200.20
Purchase #3	$87.85	11.375%	$97.8429	$97.84	$97.85	$97.80
Purchase #4	$28.56	11.492%	$31.8421	$31.84	$31.85	$31.80
Purchase #5	$144.33	4.524%	$150.8595	$150.86	$150.85	$150.90
Purchase #6	$38.36	3.162%	$39.5729	$39.57	$39.55	$39.60
Purchase #7	$246.69	5.161%	$259.4217	$259.42	$259.40	$259.40
7 purchase totals =	$926.12		$990.6286	$990.62	$990.60	$990.60