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	$94.80	4.533%	$99.0973	$99.10	$99.10	$99.10
Purchase #2	$231.79	12.641%	$261.0906	$261.09	$261.10	$261.10
Purchase #3	$101.50	7.221%	$108.8293	$108.83	$108.85	$108.80
Purchase #4	$144.56	11.663%	$161.42	$161.42	$161.40	$161.40
Purchase #5	$130.55	11.680%	$145.7982	$145.80	$145.80	$145.80
Purchase #6	$123.55	13.409%	$140.1168	$140.12	$140.10	$140.10
Purchase #7	$148.37	13.575%	$168.5112	$168.51	$168.50	$168.50
7 purchase totals =	$975.12		$1,084.8634	$1,084.87	$1,084.85	$1,084.80