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	$164.87	11.319%	$183.5316	$183.53	$183.55	$183.50
Purchase #2	$75.82	5.352%	$79.8779	$79.88	$79.90	$79.90
Purchase #3	$182.40	6.400%	$194.0736	$194.07	$194.05	$194.10
Purchase #4	$98.79	13.282%	$111.9113	$111.91	$111.90	$111.90
Purchase #5	$142.47	8.104%	$154.0158	$154.02	$154.00	$154.00
Purchase #6	$24.71	3.372%	$25.5432	$25.54	$25.55	$25.50
Purchase #7	$75.31	13.362%	$85.3729	$85.37	$85.35	$85.40
7 purchase totals =	$764.37		$834.3263	$834.32	$834.30	$834.30