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	$49.29	13.407%	$55.8983	$55.90	$55.90	$55.90
Purchase #2	$124.64	5.471%	$131.4591	$131.46	$131.45	$131.50
Purchase #3	$238.69	9.392%	$261.1078	$261.11	$261.10	$261.10
Purchase #4	$105.27	10.368%	$116.1844	$116.18	$116.20	$116.20
Purchase #5	$40.31	12.502%	$45.3496	$45.35	$45.35	$45.30
Purchase #6	$191.76	8.514%	$208.0864	$208.09	$208.10	$208.10
Purchase #7	$42.90	5.168%	$45.1171	$45.12	$45.10	$45.10
7 purchase totals =	$792.86		$863.2027	$863.21	$863.20	$863.20