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	$79.96	12.586%	$90.0238	$90.02	$90.00	$90.00
Purchase #2	$66.94	11.223%	$74.4527	$74.45	$74.45	$74.50
Purchase #3	$224.68	9.111%	$245.1506	$245.15	$245.15	$245.20
Purchase #4	$135.46	11.130%	$150.5367	$150.54	$150.55	$150.50
Purchase #5	$126.63	5.133%	$133.1299	$133.13	$133.15	$133.10
Purchase #6	$231.44	8.315%	$250.6842	$250.68	$250.70	$250.70
Purchase #7	$58.60	5.562%	$61.8593	$61.86	$61.85	$61.90
7 purchase totals =	$923.71		$1,005.8372	$1,005.83	$1,005.85	$1,005.90