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	$214.71	12.798%	$242.1886	$242.19	$242.20	$242.20
Purchase #2	$163.54	13.472%	$185.5721	$185.57	$185.55	$185.60
Purchase #3	$35.72	4.232%	$37.2317	$37.23	$37.25	$37.20
Purchase #4	$166.30	8.755%	$180.8596	$180.86	$180.85	$180.90
Purchase #5	$69.34	10.301%	$76.4827	$76.48	$76.50	$76.50
Purchase #6	$164.47	5.844%	$174.0816	$174.08	$174.10	$174.10
Purchase #7	$212.35	13.453%	$240.9174	$240.92	$240.90	$240.90
7 purchase totals =	$1,026.43		$1,137.3337	$1,137.33	$1,137.35	$1,137.40