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	$178.77	3.799%	$185.5615	$185.56	$185.55	$185.60
Purchase #2	$229.29	12.799%	$258.6368	$258.64	$258.65	$258.60
Purchase #3	$184.35	10.542%	$203.7842	$203.78	$203.80	$203.80
Purchase #4	$78.55	5.811%	$83.1145	$83.11	$83.10	$83.10
Purchase #5	$100.45	8.122%	$108.6085	$108.61	$108.60	$108.60
Purchase #6	$95.65	3.503%	$99.0006	$99.00	$99.00	$99.00
Purchase #7	$65.80	7.426%	$70.6863	$70.69	$70.70	$70.70
7 purchase totals =	$932.86		$1,009.3924	$1,009.39	$1,009.40	$1,009.40