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	$238.87	10.617%	$264.2308	$264.23	$264.25	$264.20
Purchase #2	$31.77	5.529%	$33.5266	$33.53	$33.55	$33.50
Purchase #3	$124.48	13.190%	$140.8989	$140.90	$140.90	$140.90
Purchase #4	$160.75	7.213%	$172.3449	$172.34	$172.35	$172.30
Purchase #5	$106.27	13.174%	$120.27	$120.27	$120.25	$120.30
Purchase #6	$143.52	8.855%	$156.2287	$156.23	$156.25	$156.20
Purchase #7	$54.46	4.689%	$57.0136	$57.01	$57.00	$57.00
7 purchase totals =	$860.12		$944.5135	$944.51	$944.55	$944.40