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	$100.55	8.610%	$109.2074	$109.21	$109.20	$109.20
Purchase #2	$179.56	3.737%	$186.2702	$186.27	$186.25	$186.30
Purchase #3	$151.99	9.167%	$165.9229	$165.92	$165.90	$165.90
Purchase #4	$115.29	8.217%	$124.7634	$124.76	$124.75	$124.80
Purchase #5	$68.84	4.670%	$72.0548	$72.05	$72.05	$72.10
Purchase #6	$73.72	11.736%	$82.3718	$82.37	$82.35	$82.40
Purchase #7	$73.48	10.668%	$81.3188	$81.32	$81.30	$81.30
7 purchase totals =	$763.43		$821.9093	$821.90	$821.80	$822.00