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	$77.35	6.410%	$82.3081	$82.31	$82.30	$82.30
Purchase #2	$208.32	4.683%	$218.0756	$218.08	$218.10	$218.10
Purchase #3	$174.54	10.146%	$192.2488	$192.25	$192.25	$192.20
Purchase #4	$31.93	13.780%	$36.33	$36.33	$36.35	$36.30
Purchase #5	$122.90	13.754%	$139.8037	$139.80	$139.80	$139.80
Purchase #6	$138.96	5.280%	$146.2971	$146.30	$146.30	$146.30
Purchase #7	$28.64	8.751%	$31.1463	$31.15	$31.15	$31.10
7 purchase totals =	$782.64		$846.2096	$846.22	$846.25	$846.10