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	$99.33	4.160%	$103.4621	$103.46	$103.45	$103.50
Purchase #2	$158.80	8.187%	$171.801	$171.80	$171.80	$171.80
Purchase #3	$200.88	12.235%	$225.4577	$225.46	$225.45	$225.50
Purchase #4	$61.47	7.721%	$66.2161	$66.22	$66.20	$66.20
Purchase #5	$97.86	4.586%	$102.3479	$102.35	$102.35	$102.30
Purchase #6	$141.72	6.710%	$151.2294	$151.23	$151.25	$151.20
Purchase #7	$96.97	6.690%	$103.4573	$103.46	$103.45	$103.50
7 purchase totals =	$857.03		$923.9715	$923.98	$923.95	$924.00