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	$80.50	5.649%	$85.0474	$85.05	$85.05	$85.00
Purchase #2	$82.69	9.854%	$90.8383	$90.84	$90.85	$90.80
Purchase #3	$147.96	9.686%	$162.2914	$162.29	$162.30	$162.30
Purchase #4	$211.81	4.572%	$221.494	$221.49	$221.50	$221.50
Purchase #5	$12.55	10.124%	$13.8206	$13.82	$13.80	$13.80
Purchase #6	$213.94	5.281%	$225.2382	$225.24	$225.25	$225.20
Purchase #7	$172.47	3.156%	$177.9132	$177.91	$177.90	$177.90
7 purchase totals =	$921.92		$976.6431	$976.64	$976.65	$976.50