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	$73.65	4.312%	$76.8258	$76.83	$76.85	$76.80
Purchase #2	$41.65	10.281%	$45.932	$45.93	$45.95	$45.90
Purchase #3	$92.33	6.479%	$98.3121	$98.31	$98.30	$98.30
Purchase #4	$185.90	12.188%	$208.5575	$208.56	$208.55	$208.60
Purchase #5	$83.83	3.737%	$86.9627	$86.96	$86.95	$87.00
Purchase #6	$132.64	8.674%	$144.1452	$144.15	$144.15	$144.10
Purchase #7	$211.56	8.361%	$229.2485	$229.25	$229.25	$229.20
7 purchase totals =	$821.56		$889.9838	$889.99	$890.00	$889.90