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	$159.54	7.515%	$171.5294	$171.53	$171.55	$171.50
Purchase #2	$52.53	5.812%	$55.583	$55.58	$55.60	$55.60
Purchase #3	$221.60	9.473%	$242.5922	$242.59	$242.60	$242.60
Purchase #4	$75.80	5.837%	$80.2244	$80.22	$80.20	$80.20
Purchase #5	$23.63	12.361%	$26.5509	$26.55	$26.55	$26.60
Purchase #6	$80.51	12.110%	$90.2598	$90.26	$90.25	$90.30
Purchase #7	$65.98	9.732%	$72.4012	$72.40	$72.40	$72.40
7 purchase totals =	$679.59		$739.1409	$739.13	$739.15	$739.20