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	$91.94	7.688%	$99.0083	$99.01	$99.00	$99.00
Purchase #2	$93.63	10.545%	$103.5033	$103.50	$103.50	$103.50
Purchase #3	$203.33	4.548%	$212.5774	$212.58	$212.60	$212.60
Purchase #4	$53.63	7.766%	$57.7949	$57.79	$57.80	$57.80
Purchase #5	$167.71	4.702%	$175.5957	$175.60	$175.60	$175.60
Purchase #6	$80.53	7.814%	$86.8226	$86.82	$86.80	$86.80
Purchase #7	$225.75	7.448%	$242.5639	$242.56	$242.55	$242.60
7 purchase totals =	$916.52		$977.8661	$977.86	$977.85	$977.90