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	$38.58	12.522%	$43.411	$43.41	$43.40	$43.40
Purchase #2	$191.59	7.787%	$206.5091	$206.51	$206.50	$206.50
Purchase #3	$115.51	7.821%	$124.544	$124.54	$124.55	$124.50
Purchase #4	$209.79	5.692%	$221.7312	$221.73	$221.75	$221.70
Purchase #5	$78.76	13.346%	$89.2713	$89.27	$89.25	$89.30
Purchase #6	$96.61	7.526%	$103.8809	$103.88	$103.90	$103.90
Purchase #7	$171.98	9.651%	$188.5778	$188.58	$188.60	$188.60
7 purchase totals =	$902.82		$977.9253	$977.92	$977.95	$977.90