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	$143.75	10.792%	$159.2635	$159.26	$159.25	$159.30
Purchase #2	$130.88	5.493%	$138.0692	$138.07	$138.05	$138.10
Purchase #3	$72.76	7.180%	$77.9842	$77.98	$78.00	$78.00
Purchase #4	$79.47	4.128%	$82.7505	$82.75	$82.75	$82.80
Purchase #5	$163.45	7.245%	$175.292	$175.29	$175.30	$175.30
Purchase #6	$64.35	12.404%	$72.332	$72.33	$72.35	$72.30
Purchase #7	$27.93	12.360%	$31.3821	$31.38	$31.40	$31.40
7 purchase totals =	$682.59		$737.0735	$737.06	$737.10	$737.20