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	$49.31	12.437%	$55.4427	$55.44	$55.45	$55.40
Purchase #2	$219.62	11.732%	$245.3858	$245.39	$245.40	$245.40
Purchase #3	$141.69	6.833%	$151.3717	$151.37	$151.35	$151.40
Purchase #4	$103.41	11.437%	$115.237	$115.24	$115.25	$115.20
Purchase #5	$169.53	7.241%	$181.8057	$181.81	$181.80	$181.80
Purchase #6	$171.50	8.377%	$185.8666	$185.87	$185.85	$185.90
Purchase #7	$149.60	4.770%	$156.7359	$156.74	$156.75	$156.70
7 purchase totals =	$1,004.66		$1,091.8454	$1,091.86	$1,091.85	$1,091.80