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	$80.52	10.543%	$89.0092	$89.01	$89.00	$89.00
Purchase #2	$203.42	13.836%	$231.5652	$231.57	$231.55	$231.60
Purchase #3	$84.69	5.226%	$89.1159	$89.12	$89.10	$89.10
Purchase #4	$73.94	5.160%	$77.7553	$77.76	$77.75	$77.80
Purchase #5	$184.92	6.438%	$196.8251	$196.83	$196.85	$196.80
Purchase #6	$136.83	3.869%	$142.124	$142.12	$142.10	$142.10
Purchase #7	$67.70	6.808%	$72.309	$72.31	$72.30	$72.30
7 purchase totals =	$832.02		$898.7037	$898.72	$898.65	$898.70