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	$99.65	10.203%	$109.8173	$109.82	$109.80	$109.80
Purchase #2	$148.53	9.114%	$162.067	$162.07	$162.05	$162.10
Purchase #3	$84.92	4.287%	$88.5605	$88.56	$88.55	$88.60
Purchase #4	$116.59	6.107%	$123.7102	$123.71	$123.70	$123.70
Purchase #5	$126.96	13.268%	$143.8051	$143.81	$143.80	$143.80
Purchase #6	$155.81	11.646%	$173.9556	$173.96	$173.95	$174.00
Purchase #7	$5.88	11.261%	$6.5421	$6.54	$6.55	$6.50
7 purchase totals =	$738.34		$808.4578	$808.47	$808.40	$808.50