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	$17.77	11.868%	$19.8789	$19.88	$19.90	$19.90
Purchase #2	$139.97	13.851%	$159.3572	$159.36	$159.35	$159.40
Purchase #3	$73.39	6.485%	$78.1493	$78.15	$78.15	$78.10
Purchase #4	$17.45	8.442%	$18.9231	$18.92	$18.90	$18.90
Purchase #5	$78.54	12.661%	$88.4839	$88.48	$88.50	$88.50
Purchase #6	$8.96	6.744%	$9.5643	$9.56	$9.55	$9.60
Purchase #7	$54.89	8.409%	$59.5057	$59.51	$59.50	$59.50
7 purchase totals =	$390.97		$433.8624	$433.86	$433.85	$433.90