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	$132.38	5.129%	$139.1698	$139.17	$139.15	$139.20
Purchase #2	$245.37	9.754%	$269.3034	$269.30	$269.30	$269.30
Purchase #3	$87.99	10.774%	$97.47	$97.47	$97.45	$97.50
Purchase #4	$188.59	5.221%	$198.4363	$198.44	$198.45	$198.40
Purchase #5	$22.39	13.213%	$25.3484	$25.35	$25.35	$25.30
Purchase #6	$245.33	10.797%	$271.8183	$271.82	$271.80	$271.80
Purchase #7	$13.56	10.869%	$15.0338	$15.03	$15.05	$15.00
7 purchase totals =	$935.61		$1,016.5800	$1,016.58	$1,016.55	$1,016.50