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	$247.70	5.510%	$261.3483	$261.35	$261.35	$261.30
Purchase #2	$148.86	12.454%	$167.399	$167.40	$167.40	$167.40
Purchase #3	$115.68	12.830%	$130.5217	$130.52	$130.50	$130.50
Purchase #4	$78.53	9.418%	$85.926	$85.93	$85.95	$85.90
Purchase #5	$36.74	13.705%	$41.7752	$41.78	$41.80	$41.80
Purchase #6	$65.48	7.143%	$70.1572	$70.16	$70.15	$70.20
Purchase #7	$46.86	12.738%	$52.829	$52.83	$52.85	$52.80
7 purchase totals =	$739.85		$809.9564	$809.97	$810.00	$809.90