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	$238.64	4.596%	$249.6079	$249.61	$249.60	$249.60
Purchase #2	$194.75	9.424%	$213.1032	$213.10	$213.10	$213.10
Purchase #3	$52.98	8.620%	$57.5469	$57.55	$57.55	$57.50
Purchase #4	$56.90	10.299%	$62.7601	$62.76	$62.75	$62.80
Purchase #5	$141.71	8.131%	$153.2324	$153.23	$153.25	$153.20
Purchase #6	$97.54	12.224%	$109.4633	$109.46	$109.45	$109.50
Purchase #7	$220.57	12.671%	$248.5184	$248.52	$248.50	$248.50
7 purchase totals =	$1,003.09		$1,094.2322	$1,094.23	$1,094.20	$1,094.20