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	$70.47	3.333%	$72.8188	$72.82	$72.80	$72.80
Purchase #2	$72.91	9.813%	$80.0647	$80.06	$80.05	$80.10
Purchase #3	$237.35	10.138%	$261.4125	$261.41	$261.40	$261.40
Purchase #4	$68.76	3.436%	$71.1226	$71.12	$71.10	$71.10
Purchase #5	$65.80	8.319%	$71.2739	$71.27	$71.25	$71.30
Purchase #6	$109.55	7.185%	$117.4212	$117.42	$117.40	$117.40
Purchase #7	$125.64	9.130%	$137.1109	$137.11	$137.10	$137.10
7 purchase totals =	$750.48		$811.2246	$811.21	$811.10	$811.20