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	$239.46	12.614%	$269.6655	$269.67	$269.65	$269.70
Purchase #2	$102.72	9.428%	$112.4044	$112.40	$112.40	$112.40
Purchase #3	$131.63	9.654%	$144.3376	$144.34	$144.35	$144.30
Purchase #4	$66.81	7.516%	$71.8314	$71.83	$71.85	$71.80
Purchase #5	$194.78	5.647%	$205.7792	$205.78	$205.80	$205.80
Purchase #6	$96.85	8.555%	$105.1355	$105.14	$105.15	$105.10
Purchase #7	$42.31	12.790%	$47.7214	$47.72	$47.70	$47.70
7 purchase totals =	$874.56		$956.8750	$956.88	$956.90	$956.80