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	$208.74	6.717%	$222.7611	$222.76	$222.75	$222.80
Purchase #2	$215.64	9.112%	$235.2891	$235.29	$235.30	$235.30
Purchase #3	$115.73	13.279%	$131.0978	$131.10	$131.10	$131.10
Purchase #4	$82.61	9.816%	$90.719	$90.72	$90.70	$90.70
Purchase #5	$122.90	13.685%	$139.7189	$139.72	$139.70	$139.70
Purchase #6	$226.39	13.774%	$257.573	$257.57	$257.55	$257.60
Purchase #7	$244.36	12.322%	$274.47	$274.47	$274.45	$274.50
7 purchase totals =	$1,216.37		$1,351.6289	$1,351.63	$1,351.55	$1,351.70