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	$229.31	6.215%	$243.5616	$243.56	$243.55	$243.60
Purchase #2	$182.77	4.672%	$191.309	$191.31	$191.30	$191.30
Purchase #3	$78.31	4.672%	$81.9686	$81.97	$81.95	$82.00
Purchase #4	$151.46	9.307%	$165.5564	$165.56	$165.55	$165.60
Purchase #5	$39.37	13.126%	$44.5377	$44.54	$44.55	$44.50
Purchase #6	$174.66	6.754%	$186.4565	$186.46	$186.45	$186.50
Purchase #7	$155.55	13.362%	$176.3346	$176.33	$176.35	$176.30
7 purchase totals =	$1,011.43		$1,089.7244	$1,089.73	$1,089.70	$1,089.80