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	$167.29	12.695%	$188.5275	$188.53	$188.55	$188.50
Purchase #2	$72.29	8.866%	$78.6992	$78.70	$78.70	$78.70
Purchase #3	$135.57	11.253%	$150.8257	$150.83	$150.85	$150.80
Purchase #4	$82.76	5.108%	$86.9874	$86.99	$87.00	$87.00
Purchase #5	$26.49	13.592%	$30.0905	$30.09	$30.10	$30.10
Purchase #6	$171.83	6.272%	$182.6072	$182.61	$182.60	$182.60
Purchase #7	$203.38	9.245%	$222.1825	$222.18	$222.20	$222.20
7 purchase totals =	$859.61		$939.9200	$939.93	$940.00	$939.90