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	$63.65	12.867%	$71.8398	$71.84	$71.85	$71.80
Purchase #2	$50.91	12.735%	$57.3934	$57.39	$57.40	$57.40
Purchase #3	$75.28	9.530%	$82.4542	$82.45	$82.45	$82.50
Purchase #4	$221.51	12.219%	$248.5763	$248.58	$248.60	$248.60
Purchase #5	$207.76	6.805%	$221.8981	$221.90	$221.90	$221.90
Purchase #6	$179.90	3.303%	$185.8421	$185.84	$185.85	$185.80
Purchase #7	$218.76	12.361%	$245.8009	$245.80	$245.80	$245.80
7 purchase totals =	$1,017.77		$1,113.8048	$1,113.80	$1,113.85	$1,113.80