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	$123.85	4.841%	$129.8456	$129.85	$129.85	$129.80
Purchase #2	$120.89	13.180%	$136.8233	$136.82	$136.80	$136.80
Purchase #3	$75.68	6.361%	$80.494	$80.49	$80.50	$80.50
Purchase #4	$160.27	7.468%	$172.239	$172.24	$172.25	$172.20
Purchase #5	$172.26	5.673%	$182.0323	$182.03	$182.05	$182.00
Purchase #6	$178.91	11.234%	$199.0087	$199.01	$199.00	$199.00
Purchase #7	$73.31	12.666%	$82.5954	$82.60	$82.60	$82.60
7 purchase totals =	$905.17		$983.0383	$983.04	$983.05	$982.90