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	$111.88	11.598%	$124.8558	$124.86	$124.85	$124.90
Purchase #2	$131.41	9.112%	$143.3841	$143.38	$143.40	$143.40
Purchase #3	$59.91	6.759%	$63.9593	$63.96	$63.95	$64.00
Purchase #4	$37.56	11.801%	$41.9925	$41.99	$42.00	$42.00
Purchase #5	$101.57	3.508%	$105.1331	$105.13	$105.15	$105.10
Purchase #6	$209.80	4.849%	$219.9732	$219.97	$219.95	$220.00
Purchase #7	$124.60	9.493%	$136.4283	$136.43	$136.45	$136.40
7 purchase totals =	$776.73		$835.7263	$835.72	$835.75	$835.80