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	$185.60	10.395%	$204.8931	$204.89	$204.90	$204.90
Purchase #2	$37.66	13.677%	$42.8108	$42.81	$42.80	$42.80
Purchase #3	$237.67	3.416%	$245.7888	$245.79	$245.80	$245.80
Purchase #4	$80.49	11.168%	$89.4791	$89.48	$89.50	$89.50
Purchase #5	$195.80	12.589%	$220.4493	$220.45	$220.45	$220.40
Purchase #6	$78.40	8.604%	$85.1455	$85.15	$85.15	$85.10
Purchase #7	$185.76	5.493%	$195.9638	$195.96	$195.95	$196.00
7 purchase totals =	$1,001.38		$1,084.5304	$1,084.53	$1,084.55	$1,084.50