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	$25.89	7.426%	$27.8126	$27.81	$27.80	$27.80
Purchase #2	$82.33	3.747%	$85.4149	$85.41	$85.40	$85.40
Purchase #3	$244.66	4.326%	$255.244	$255.24	$255.25	$255.20
Purchase #4	$152.81	13.692%	$173.7327	$173.73	$173.75	$173.70
Purchase #5	$130.73	4.365%	$136.4364	$136.44	$136.45	$136.40
Purchase #6	$43.46	4.302%	$45.3296	$45.33	$45.35	$45.30
Purchase #7	$84.94	10.690%	$94.0201	$94.02	$94.00	$94.00
7 purchase totals =	$764.82		$817.9903	$817.98	$818.00	$817.80