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	$11.50	4.192%	$11.9821	$11.98	$12.00	$12.00
Purchase #2	$143.78	8.767%	$156.3852	$156.39	$156.40	$156.40
Purchase #3	$49.55	11.819%	$55.4063	$55.41	$55.40	$55.40
Purchase #4	$224.99	9.217%	$245.7273	$245.73	$245.75	$245.70
Purchase #5	$249.46	9.601%	$273.4107	$273.41	$273.40	$273.40
Purchase #6	$85.79	10.258%	$94.5903	$94.59	$94.60	$94.60
Purchase #7	$51.31	3.301%	$53.0037	$53.00	$53.00	$53.00
7 purchase totals =	$816.38		$890.5056	$890.51	$890.55	$890.50