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	$178.54	3.233%	$184.3122	$184.31	$184.30	$184.30
Purchase #2	$125.53	6.565%	$133.771	$133.77	$133.75	$133.80
Purchase #3	$147.78	6.109%	$156.8079	$156.81	$156.80	$156.80
Purchase #4	$86.92	3.306%	$89.7936	$89.79	$89.80	$89.80
Purchase #5	$136.79	8.543%	$148.476	$148.48	$148.50	$148.50
Purchase #6	$74.99	9.795%	$82.3353	$82.34	$82.35	$82.30
Purchase #7	$172.36	9.847%	$189.3323	$189.33	$189.35	$189.30
7 purchase totals =	$922.91		$984.8283	$984.83	$984.85	$984.80