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	$106.50	9.554%	$116.675	$116.68	$116.70	$116.70
Purchase #2	$77.57	10.299%	$85.5589	$85.56	$85.55	$85.60
Purchase #3	$77.92	7.125%	$83.4718	$83.47	$83.45	$83.50
Purchase #4	$95.97	9.288%	$104.8837	$104.88	$104.90	$104.90
Purchase #5	$55.90	3.543%	$57.8805	$57.88	$57.90	$57.90
Purchase #6	$78.93	8.698%	$85.7953	$85.80	$85.80	$85.80
Purchase #7	$131.98	5.288%	$138.9591	$138.96	$138.95	$139.00
7 purchase totals =	$624.77		$673.2243	$673.23	$673.25	$673.40