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	$82.78	4.383%	$86.4082	$86.41	$86.40	$86.40
Purchase #2	$158.95	7.163%	$170.3356	$170.34	$170.35	$170.30
Purchase #3	$137.80	5.457%	$145.3197	$145.32	$145.30	$145.30
Purchase #4	$140.84	7.728%	$151.7241	$151.72	$151.70	$151.70
Purchase #5	$36.35	9.760%	$39.8978	$39.90	$39.90	$39.90
Purchase #6	$65.90	9.768%	$72.3371	$72.34	$72.35	$72.30
Purchase #7	$170.55	8.527%	$185.0928	$185.09	$185.10	$185.10
7 purchase totals =	$793.17		$851.1153	$851.12	$851.10	$851.00