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	$134.41	7.821%	$144.9222	$144.92	$144.90	$144.90
Purchase #2	$150.57	6.720%	$160.6883	$160.69	$160.70	$160.70
Purchase #3	$59.50	5.226%	$62.6095	$62.61	$62.60	$62.60
Purchase #4	$192.71	9.814%	$211.6226	$211.62	$211.60	$211.60
Purchase #5	$203.90	10.760%	$225.8396	$225.84	$225.85	$225.80
Purchase #6	$176.56	9.867%	$193.9812	$193.98	$194.00	$194.00
Purchase #7	$80.72	13.217%	$91.3888	$91.39	$91.40	$91.40
7 purchase totals =	$998.37		$1,091.0522	$1,091.05	$1,091.05	$1,091.00