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	$75.32	10.554%	$83.2693	$83.27	$83.25	$83.30
Purchase #2	$249.59	8.779%	$271.5015	$271.50	$271.50	$271.50
Purchase #3	$141.52	7.579%	$152.2458	$152.25	$152.25	$152.20
Purchase #4	$219.96	13.366%	$249.3599	$249.36	$249.35	$249.40
Purchase #5	$76.91	7.552%	$82.7182	$82.72	$82.70	$82.70
Purchase #6	$130.37	5.642%	$137.7255	$137.73	$137.75	$137.70
Purchase #7	$64.62	13.187%	$73.1414	$73.14	$73.15	$73.10
7 purchase totals =	$958.29		$1,049.9616	$1,049.97	$1,049.95	$1,049.90