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	$37.59	8.118%	$40.6416	$40.64	$40.65	$40.60
Purchase #2	$218.35	12.439%	$245.5106	$245.51	$245.50	$245.50
Purchase #3	$94.64	5.255%	$99.6133	$99.61	$99.60	$99.60
Purchase #4	$188.95	9.292%	$206.5072	$206.51	$206.50	$206.50
Purchase #5	$173.49	7.132%	$185.8633	$185.86	$185.85	$185.90
Purchase #6	$188.85	12.804%	$213.0304	$213.03	$213.05	$213.00
Purchase #7	$229.75	13.346%	$260.4124	$260.41	$260.40	$260.40
7 purchase totals =	$1,131.62		$1,251.5788	$1,251.57	$1,251.55	$1,251.50