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	$239.99	10.547%	$265.3017	$265.30	$265.30	$265.30
Purchase #2	$136.69	12.791%	$154.174	$154.17	$154.15	$154.20
Purchase #3	$166.64	11.454%	$185.7269	$185.73	$185.75	$185.70
Purchase #4	$28.93	12.823%	$32.6397	$32.64	$32.65	$32.60
Purchase #5	$170.34	6.813%	$181.9453	$181.95	$181.95	$181.90
Purchase #6	$98.61	10.724%	$109.1849	$109.18	$109.20	$109.20
Purchase #7	$144.32	4.666%	$151.054	$151.05	$151.05	$151.10
7 purchase totals =	$985.52		$1,080.0265	$1,080.02	$1,080.05	$1,080.00