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	$169.35	3.179%	$174.7336	$174.73	$174.75	$174.70
Purchase #2	$154.63	3.128%	$159.4668	$159.47	$159.45	$159.50
Purchase #3	$90.92	13.718%	$103.3924	$103.39	$103.40	$103.40
Purchase #4	$58.41	8.627%	$63.449	$63.45	$63.45	$63.40
Purchase #5	$234.70	12.179%	$263.2841	$263.28	$263.30	$263.30
Purchase #6	$97.29	12.559%	$109.5087	$109.51	$109.50	$109.50
Purchase #7	$85.60	13.276%	$96.9643	$96.96	$96.95	$97.00
7 purchase totals =	$890.90		$970.7989	$970.79	$970.80	$970.80