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	$108.54	13.385%	$123.0681	$123.07	$123.05	$123.10
Purchase #2	$89.27	10.790%	$98.9022	$98.90	$98.90	$98.90
Purchase #3	$54.50	5.216%	$57.3427	$57.34	$57.35	$57.30
Purchase #4	$96.83	10.802%	$107.2896	$107.29	$107.30	$107.30
Purchase #5	$121.54	5.598%	$128.3438	$128.34	$128.35	$128.30
Purchase #6	$71.70	6.194%	$76.1411	$76.14	$76.15	$76.10
Purchase #7	$163.31	11.646%	$182.3291	$182.33	$182.35	$182.30
7 purchase totals =	$705.69		$773.4166	$773.41	$773.45	$773.30