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	$90.69	13.504%	$102.9368	$102.94	$102.95	$102.90
Purchase #2	$74.53	8.399%	$80.7898	$80.79	$80.80	$80.80
Purchase #3	$249.63	12.483%	$280.7913	$280.79	$280.80	$280.80
Purchase #4	$177.80	6.792%	$189.8762	$189.88	$189.90	$189.90
Purchase #5	$151.35	5.809%	$160.1419	$160.14	$160.15	$160.10
Purchase #6	$168.25	13.870%	$191.5863	$191.59	$191.60	$191.60
Purchase #7	$236.83	13.644%	$269.1431	$269.14	$269.15	$269.10
7 purchase totals =	$1,149.08		$1,275.2654	$1,275.27	$1,275.35	$1,275.20