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	$157.93	10.407%	$174.3658	$174.37	$174.35	$174.40
Purchase #2	$68.43	10.301%	$75.479	$75.48	$75.50	$75.50
Purchase #3	$94.43	9.460%	$103.3631	$103.36	$103.35	$103.40
Purchase #4	$178.60	9.802%	$196.1064	$196.11	$196.10	$196.10
Purchase #5	$96.71	6.582%	$103.0755	$103.08	$103.10	$103.10
Purchase #6	$65.25	12.569%	$73.4513	$73.45	$73.45	$73.50
Purchase #7	$99.33	4.740%	$104.0382	$104.04	$104.05	$104.00
7 purchase totals =	$760.68		$829.8793	$829.89	$829.90	$830.00