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	$17.69	5.777%	$18.712	$18.71	$18.70	$18.70
Purchase #2	$23.41	10.642%	$25.9013	$25.90	$25.90	$25.90
Purchase #3	$220.98	12.152%	$247.8335	$247.83	$247.85	$247.80
Purchase #4	$72.45	8.646%	$78.714	$78.71	$78.70	$78.70
Purchase #5	$86.27	9.869%	$94.784	$94.78	$94.80	$94.80
Purchase #6	$55.67	10.136%	$61.3127	$61.31	$61.30	$61.30
Purchase #7	$232.41	5.664%	$245.5737	$245.57	$245.55	$245.60
7 purchase totals =	$708.88		$772.8312	$772.81	$772.80	$772.80