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	$136.60	12.587%	$153.7938	$153.79	$153.80	$153.80
Purchase #2	$144.90	6.699%	$154.6069	$154.61	$154.60	$154.60
Purchase #3	$41.90	7.700%	$45.1263	$45.13	$45.15	$45.10
Purchase #4	$96.48	3.410%	$99.77	$99.77	$99.75	$99.80
Purchase #5	$168.32	12.543%	$189.4324	$189.43	$189.45	$189.40
Purchase #6	$102.88	11.585%	$114.7986	$114.80	$114.80	$114.80
Purchase #7	$175.96	6.499%	$187.3956	$187.40	$187.40	$187.40
7 purchase totals =	$867.04		$944.9236	$944.93	$944.95	$944.90