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	$42.43	3.418%	$43.8803	$43.88	$43.90	$43.90
Purchase #2	$56.91	5.508%	$60.0446	$60.04	$60.05	$60.00
Purchase #3	$139.35	12.451%	$156.7005	$156.70	$156.70	$156.70
Purchase #4	$185.58	5.336%	$195.4825	$195.48	$195.50	$195.50
Purchase #5	$183.33	9.341%	$200.4549	$200.45	$200.45	$200.50
Purchase #6	$249.96	11.802%	$279.4603	$279.46	$279.45	$279.50
Purchase #7	$129.64	9.546%	$142.0154	$142.02	$142.00	$142.00
7 purchase totals =	$987.20		$1,078.0385	$1,078.03	$1,078.05	$1,078.10