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	$131.79	10.105%	$145.1074	$145.11	$145.10	$145.10
Purchase #2	$57.55	3.352%	$59.4791	$59.48	$59.50	$59.50
Purchase #3	$38.66	9.398%	$42.2933	$42.29	$42.30	$42.30
Purchase #4	$192.57	12.410%	$216.4679	$216.47	$216.45	$216.50
Purchase #5	$91.85	7.789%	$99.0042	$99.00	$99.00	$99.00
Purchase #6	$212.28	12.450%	$238.7089	$238.71	$238.70	$238.70
Purchase #7	$160.28	9.327%	$175.2293	$175.23	$175.25	$175.20
7 purchase totals =	$884.98		$976.2901	$976.29	$976.30	$976.30