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	$63.53	12.408%	$71.4128	$71.41	$71.40	$71.40
Purchase #2	$196.52	11.378%	$218.88	$218.88	$218.90	$218.90
Purchase #3	$246.86	8.460%	$267.7444	$267.74	$267.75	$267.70
Purchase #4	$165.82	12.119%	$185.9157	$185.92	$185.90	$185.90
Purchase #5	$148.96	3.631%	$154.3687	$154.37	$154.35	$154.40
Purchase #6	$195.45	11.292%	$217.5202	$217.52	$217.50	$217.50
Purchase #7	$196.82	11.829%	$220.1018	$220.10	$220.10	$220.10
7 purchase totals =	$1,213.96		$1,335.9436	$1,335.94	$1,335.90	$1,335.90