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	$28.96	9.685%	$31.7648	$31.76	$31.75	$31.80
Purchase #2	$97.36	6.668%	$103.852	$103.85	$103.85	$103.90
Purchase #3	$84.53	6.429%	$89.9644	$89.96	$89.95	$90.00
Purchase #4	$86.57	11.452%	$96.484	$96.48	$96.50	$96.50
Purchase #5	$24.65	6.699%	$26.3013	$26.30	$26.30	$26.30
Purchase #6	$83.64	7.500%	$89.913	$89.91	$89.90	$89.90
Purchase #7	$181.31	5.273%	$190.8705	$190.87	$190.85	$190.90
7 purchase totals =	$587.02		$629.1500	$629.13	$629.10	$629.30