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	$65.69	8.296%	$71.1396	$71.14	$71.15	$71.10
Purchase #2	$250.92	8.822%	$273.0562	$273.06	$273.05	$273.10
Purchase #3	$104.84	11.293%	$116.6796	$116.68	$116.70	$116.70
Purchase #4	$184.59	6.689%	$196.9372	$196.94	$196.95	$196.90
Purchase #5	$8.63	9.296%	$9.4322	$9.43	$9.45	$9.40
Purchase #6	$93.35	9.460%	$102.1809	$102.18	$102.20	$102.20
Purchase #7	$80.71	11.111%	$89.6777	$89.68	$89.70	$89.70
7 purchase totals =	$788.73		$859.1034	$859.11	$859.20	$859.10