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	$249.67	12.247%	$280.2471	$280.25	$280.25	$280.20
Purchase #2	$195.50	12.259%	$219.4663	$219.47	$219.45	$219.50
Purchase #3	$74.37	6.124%	$78.9244	$78.92	$78.90	$78.90
Purchase #4	$92.76	6.375%	$98.6735	$98.67	$98.65	$98.70
Purchase #5	$136.65	6.349%	$145.3259	$145.33	$145.35	$145.30
Purchase #6	$84.49	7.496%	$90.8234	$90.82	$90.80	$90.80
Purchase #7	$102.92	13.407%	$116.7185	$116.72	$116.70	$116.70
7 purchase totals =	$936.36		$1,030.1791	$1,030.18	$1,030.10	$1,030.10