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	$103.51	5.763%	$109.4753	$109.48	$109.50	$109.50
Purchase #2	$183.95	4.833%	$192.8403	$192.84	$192.85	$192.80
Purchase #3	$169.78	10.358%	$187.3658	$187.37	$187.35	$187.40
Purchase #4	$18.31	12.352%	$20.5717	$20.57	$20.55	$20.60
Purchase #5	$75.27	7.428%	$80.8611	$80.86	$80.85	$80.90
Purchase #6	$223.28	11.111%	$248.0886	$248.09	$248.10	$248.10
Purchase #7	$59.39	9.656%	$65.1247	$65.12	$65.10	$65.10
7 purchase totals =	$833.49		$904.3275	$904.33	$904.30	$904.40